diff --git a/Cargo.toml b/Cargo.toml
index bc079115..044eefea 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -35,18 +35,15 @@ axum = { version = "0.7", default-features = false, features = [
   "json",
   "matched-path",
 ], optional = true }
-axum-extra = { version = "0.9", features = ["cookie", "typed-header"] }
+axum-extra = { version = "0.9", features = ["typed-header", "cookie"] }
 axum-server = { version = "0.6", features = ["tls-rustls"] }
 tower = { version = "0.4.13", features = ["util"] }
-# tower-http = { version = "0.5", features = [
-#   "add-extension",
-#   "cors",
-#   "sensitive-headers",
-#   "trace",
-#   "util",
-# ] }
 tower-http = { version = "0.5", features = [
-  "full",
+  "add-extension",
+  "cors",
+  "sensitive-headers",
+  "trace",
+  "util",
 ] }
 tower-service = "0.3"
 
@@ -143,6 +140,7 @@ figment = { version = "0.10.8", features = ["env", "toml"] }
 # Validating urls in config
 url = { version = "2", features = ["serde"] }
 
+mas-oidc-client = { version = "0.9", default-features = false, features = ["hyper"] }
 # HTML
 maud = { version = "0.26.0", default-features = false, features = ["axum"] }
 
@@ -152,19 +150,14 @@ tikv-jemallocator = { version = "0.5.0", features = [
 ], optional = true }
 
 sd-notify = { version = "0.4.1", optional = true }
-http-body-util = "0.1.2"
-hyper-rustls = { version = "0.27.2", default-features = false, features = ["http1", "http2", "ring", "rustls-native-certs", "rustls-platform-verifier"] }
-mas-http = "0.9.0"
 
 # Used for matrix spec type definitions and helpers
 [dependencies.ruma]
 features = [
   "appservice-api-c",
-  "client",
   "client-api",
   "compat",
   "federation-api",
-  "client-hyper",
   "push-gateway-api-c",
   "rand",
   "ring-compat",
@@ -183,16 +176,11 @@ optional = true
 package = "rust-rocksdb"
 version = "0.25"
 
-# Used for Single Sign-On
-[dependencies.mas-oidc-client]
-git = "https://github.com/matrix-org/matrix-authentication-service.git"
-default-features = false
-
 [target.'cfg(unix)'.dependencies]
 nix = { version = "0.28", features = ["resource"] }
 
 [features]
-default = ["backend_rocksdb", "backend_sqlite", "conduit_bin", "systemd"]
+default = ["backend_sqlite", "conduit_bin"]
 #backend_sled = ["sled"]
 backend_persy = ["parking_lot", "persy"]
 backend_sqlite = ["sqlite"]
diff --git a/src/api/client_server/session.rs b/src/api/client_server/session.rs
index aea8d3ac..148c67f5 100644
--- a/src/api/client_server/session.rs
+++ b/src/api/client_server/session.rs
@@ -1,5 +1,6 @@
 use super::{DEVICE_ID_LENGTH, TOKEN_LENGTH};
 use crate::{service::sso::LoginToken, services, utils, Error, Result, Ruma};
+use jsonwebtoken::{Algorithm, Validation};
 use ruma::{
     api::client::{
         error::ErrorKind,
@@ -24,17 +25,16 @@ struct Claims {
 pub async fn get_login_types_route(
     _body: Ruma<get_login_types::v3::Request>,
 ) -> Result<get_login_types::v3::Response> {
+    let identity_providers: Vec<_> = services().sso.login_type().collect();
     let mut flows = vec![
         get_login_types::v3::LoginType::Password(Default::default()),
         get_login_types::v3::LoginType::ApplicationService(Default::default()),
     ];
 
-    if let v @ [_, ..] = &*services().sso.flows() {
-        let flow = get_login_types::v3::SsoLoginType {
-            identity_providers: v.to_owned(),
-        };
-
-        flows.push(get_login_types::v3::LoginType::Sso(flow));
+    if !identity_providers.is_empty() {
+        flows.push(get_login_types::v3::LoginType::Sso(
+            get_login_types::v3::SsoLoginType { identity_providers },
+        ));
     }
 
     Ok(get_login_types::v3::Response::new(flows))
@@ -113,30 +113,26 @@ pub async fn login_route(body: Ruma<login::v3::Request>) -> Result<login::v3::Re
         login::v3::LoginInfo::Token(login::v3::Token { token }) => {
             match (
                 services().globals.jwt_decoding_key(),
-                &services().sso.providers().is_empty(),
+                services().sso.login_type().next().is_some(),
             ) {
                 (_, false) => {
-                    let mut validation =
-                        jsonwebtoken::Validation::new(jsonwebtoken::Algorithm::HS256);
+                    let mut validation = Validation::new(Algorithm::HS256);
                     validation.validate_nbf = false;
                     validation.set_required_spec_claims(&["sub", "exp", "aud", "iss"]);
 
-                    let login_token = services()
+                    services()
                         .globals
                         .validate_claims::<LoginToken>(token, Some(validation))
-                        .map_err(|_| {
-                            Error::BadRequest(ErrorKind::InvalidParam, "Invalid token.")
-                        })?;
-
-                    login_token.audience().map_err(|_| {
-                        Error::BadRequest(ErrorKind::InvalidParam, "Invalid token audience.")
-                    })?
+                        .as_ref()
+                        .map(LoginToken::audience)
+                        .map(ToOwned::to_owned)
+                        .map_err(|_| Error::BadRequest(ErrorKind::InvalidParam, "Invalid token."))?
                 }
                 (Some(jwt_decoding_key), _) => {
                     let token = jsonwebtoken::decode::<Claims>(
                         token,
                         jwt_decoding_key,
-                        &jsonwebtoken::Validation::default(),
+                        &Validation::default(),
                     )
                     .map_err(|_| {
                         Error::BadRequest(ErrorKind::InvalidUsername, "Token is invalid.")
diff --git a/src/api/client_server/sso.rs b/src/api/client_server/sso.rs
index c6d26d27..c5e3b0e3 100644
--- a/src/api/client_server/sso.rs
+++ b/src/api/client_server/sso.rs
@@ -1,30 +1,24 @@
 use std::{borrow::Borrow, collections::HashMap, iter::Iterator, time::SystemTime};
 
 use crate::{
-    config::{
-        sso::{Registration, Template},
-        IdpConfig,
-    },
+    config::IdpConfig,
     service::sso::{
-        templates, LoginToken, RegistrationInfo, RegistrationToken, ValidationData,
-        REGISTRATION_EXPIRATION_SECS, SESSION_EXPIRATION_SECS, SSO_AUTH_EXPIRATION_SECS,
-        SSO_SESSION_COOKIE,
+        LoginToken, ValidationData, SSO_AUTH_EXPIRATION_SECS, SSO_SESSION_COOKIE, SUBJECT_CLAIM_KEY,
     },
     services, utils, Error, Result, Ruma,
 };
 use axum::{
-    extract::RawQuery,
     response::{AppendHeaders, IntoResponse, Redirect},
     RequestExt,
 };
 use axum_extra::{
-    headers::{self, HeaderMapExt},
+    headers::{self},
     TypedHeader,
 };
 use http::header;
 use mas_oidc_client::{
     requests::{
-        authorization_code::{self, AuthorizationRequestData, AuthorizationValidationData},
+        authorization_code::{self, AuthorizationRequestData},
         jose::{self, JwtVerificationData},
         userinfo,
     },
@@ -35,17 +29,17 @@ use mas_oidc_client::{
         requests::{AccessTokenResponse, AuthorizationResponse},
     },
 };
-use rand::{rngs::StdRng, SeedableRng};
+use rand::{rngs::StdRng, Rng, SeedableRng};
 use ruma::{
     api::client::{
         error::ErrorKind,
-        session::{self, sso_login, sso_login_with_provider},
+        session::{sso_login, sso_login_with_provider},
     },
-    events::GlobalAccountDataEventType,
-    push, OwnedMxcUri, UserId,
+    events::{room::message::RoomMessageEventContent, GlobalAccountDataEventType},
+    push, UserId,
 };
-use serde_json::Number;
-use tracing::error;
+use serde_json::Value;
+use tracing::{error, info, warn};
 use url::Url;
 
 pub const CALLBACK_PATH: &str = "_matrix/client/unstable/sso/callback";
@@ -54,17 +48,28 @@ pub const CALLBACK_PATH: &str = "_matrix/client/unstable/sso/callback";
 ///
 /// Redirect the user to the SSO interface.
 /// TODO: this should be removed once Ruma supports trailing slashes.
-pub async fn get_sso_redirect(
-    body: Ruma<sso_login::v3::Request>,
+pub async fn get_sso_redirect_route(
+    Ruma {
+        body,
+        sender_user,
+        sender_device,
+        sender_servername,
+        json_body,
+        ..
+    }: Ruma<sso_login::v3::Request>,
 ) -> Result<sso_login::v3::Response> {
     let sso_login_with_provider::v3::Response { location, cookie } =
-        get_sso_redirect_with_provider(
+        get_sso_redirect_with_provider_route(
             Ruma {
                 body: sso_login_with_provider::v3::Request::new(
                     Default::default(),
-                    body.redirect_url.clone(),
+                    body.redirect_url,
                 ),
-                ..body
+                sender_user,
+                sender_device,
+                sender_servername,
+                json_body,
+                appservice_info: None,
             }
             .into(),
         )
@@ -76,7 +81,7 @@ pub async fn get_sso_redirect(
 /// # `GET /_matrix/client/v3/login/sso/redirect/{idpId}`
 ///
 /// Redirects the user to the SSO interface.
-pub async fn get_sso_redirect_with_provider(
+pub async fn get_sso_redirect_with_provider_route(
     body: Ruma<sso_login_with_provider::v3::Request>,
 ) -> Result<sso_login_with_provider::v3::Response> {
     let idp_ids: Vec<&str> = services()
@@ -124,7 +129,7 @@ pub async fn get_sso_redirect_with_provider(
     .map_err(|_| Error::BadRequest(ErrorKind::Unknown, "Failed to build authorization_url."))?;
 
     let signed = services().globals.sign_claims(&ValidationData::new(
-        provider.borrow().to_string(),
+        Borrow::<str>::borrow(provider).to_owned(),
         validation_data,
     ));
 
@@ -142,12 +147,7 @@ pub async fn get_sso_redirect_with_provider(
     })
 }
 
-/// # `GET /_conduit/client/sso/callback`
-///
-/// Validate the authorization response received from the identity provider.
-/// On success, generate a login token, add it to `redirectUrl` as a query and perform the redirect.
-/// If this is the first login, register the user, possibly interactively through a fallback page.
-pub async fn get_sso_callback(req: axum::extract::Request) -> Result<axum::response::Response> {
+async fn handle_callback_helper(req: axum::extract::Request) -> Result<axum::response::Response> {
     let query = req.uri().query().ok_or_else(|| {
         Error::BadRequest(ErrorKind::MissingParam, "Empty authorization callback.")
     })?;
@@ -158,22 +158,26 @@ pub async fn get_sso_callback(req: axum::extract::Request) -> Result<axum::respo
         token_type,
         id_token,
         expires_in,
-    } = serde_html_form::from_str::<AuthorizationResponse>(query).map_err(|_| {
-        serde_html_form::from_str::<ClientError>(query).unwrap_or_else(|_| {
-            error!("Failed to deserialize authorization callback: {}", callback);
+    } = serde_html_form::from_str(query).map_err(|_| {
+        serde_html_form::from_str(query)
+            .map(ClientError::into)
+            .unwrap_or_else(|_| {
+                error!("Failed to deserialize authorization callback: {}", query);
 
-            Error::BadRequest(
-                ErrorKind::Unknown,
-                "Failed to deserialize authorization callback.",
-            )
-        })
+                Error::BadRequest(
+                    ErrorKind::Unknown,
+                    "Failed to deserialize authorization callback.",
+                )
+            })
     })?;
 
-    let cookie = req
-        .extract::<Option<TypedHeader<headers::Cookie>>>()
-        .await
-        .map_err(|_| Error::BadRequest(ErrorKind::InvalidParam, "Invalid session cookie."))?
-        .ok_or_else(|_| Error::BadRequest(ErrorKind::MissingParam, "Missing session cookie."))?;
+    let Ok(Some(cookie)): Result<Option<TypedHeader<headers::Cookie>>, _> = req.extract().await
+    else {
+        return Err(Error::BadRequest(
+            ErrorKind::MissingParam,
+            "Missing session cookie.",
+        ));
+    };
 
     let ValidationData {
         provider,
@@ -186,11 +190,11 @@ pub async fn get_sso_callback(req: axum::extract::Request) -> Result<axum::respo
             })?,
             None,
         )
-        .map_err(|e| {
+        .map_err(|_| {
             Error::BadRequest(ErrorKind::InvalidParam, "Invalid value for session cookie.")
         })?;
 
-    let provider = services().sso.get(&provider).ok_or_else(|e| {
+    let provider = services().sso.get(&provider).ok_or_else(|| {
         Error::BadRequest(
             ErrorKind::InvalidParam,
             "Unknown provider for session cookie.",
@@ -204,7 +208,7 @@ pub async fn get_sso_callback(req: axum::extract::Request) -> Result<axum::respo
         ..
     } = provider.config.clone();
 
-    let credentials = match &auth_method {
+    let credentials = match &*auth_method {
         "basic" => ClientCredentials::ClientSecretBasic {
             client_id,
             client_secret,
@@ -215,6 +219,16 @@ pub async fn get_sso_callback(req: axum::extract::Request) -> Result<axum::respo
         },
         _ => todo!(),
     };
+    let ref jwks = jose::fetch_jwks(services().sso.service(), provider.metadata.jwks_uri())
+        .await
+        .map_err(|_| Error::bad_config("Failed to fetch signing keys for token endpoint."))?;
+    let jwt_verification_data = Some(JwtVerificationData {
+        jwks,
+        issuer: &provider.config.issuer,
+        client_id: &provider.config.client_id,
+        signing_algorithm: &JsonWebSignatureAlg::Rs256,
+    });
+
     let (
         AccessTokenResponse {
             access_token,
@@ -227,34 +241,22 @@ pub async fn get_sso_callback(req: axum::extract::Request) -> Result<axum::respo
         Some(id_token),
     ) = authorization_code::access_token_with_authorization_code(
         services().sso.service(),
-        method,
+        credentials,
         provider.metadata.token_endpoint(),
-        code,
-        validation_data,
+        code.unwrap_or_default(),
+        validation_data.clone(),
         jwt_verification_data,
         SystemTime::now().into(),
         &mut StdRng::from_entropy(),
     )
     .await
-    .map_err(|e| Error::bad_config("Failed to fetch access token."))?
+    .map_err(|_| Error::bad_config("Failed to fetch access token."))?
     else {
         unreachable!("ID token should never be empty")
     };
 
-    // let userinfo = provider.fetch_userinfo(&access_token, &id_token).await?;
-
     let mut userinfo = HashMap::default();
     if let Some(endpoint) = &provider.metadata.userinfo_endpoint {
-        let ref jwks = jose::fetch_jwks(services().sso.service(), provider.metadata.jwks_uri())
-            .await
-            .map_err(|e| Error::bad_config("Failed to fetch signing keys for token endpoint."))?;
-        let jwt_verification_data = Some(JwtVerificationData {
-            jwks,
-            issuer: &provider.config.issuer,
-            client_id: credentials.client_id(),
-            signing_algorithm: &JsonWebSignatureAlg::Rs256,
-        });
-
         userinfo = userinfo::fetch_userinfo(
             services().sso.service(),
             endpoint,
@@ -263,386 +265,133 @@ pub async fn get_sso_callback(req: axum::extract::Request) -> Result<axum::respo
             &id_token,
         )
         .await
-        .map_err(|e| Error::bad_config("Failed to fetch claims for userinfo endpoint."))?;
+        .map_err(|_| Error::bad_config("Failed to fetch claims for userinfo endpoint."))?;
     };
 
-    let (_, mut claims) = id_token.into_parts();
+    let (_, id_token) = id_token.into_parts();
 
-    let subject = claims.get("sub").ok_or_else(|| {
-        error!("Unique \"sub\" claim is missing from ID token: {claims:?}");
-
-        Error::bad_config("Unique \"sub\" claim is missing from ID token.")
-    })?;
-
-    let subject = &subject
-        .as_str()
-        .map(str::to_owned)
-        .or_else(|| subject.as_number().map(Number::to_string))
-        .expect("unique claim should be a string or number");
-
-    let redirect_uri = &validation_data.redirect_uri;
-
-    if let Some(user_id) = services()
-        .sso
-        .user_from_claim(&validation_data.provider_id, subject)?
-    {
-        let login_token = LoginToken::new(validation_data.provider_id.to_owned(), user_id);
-
-        let redirect_uri = redirect_with_login_token(redirect_uri.to_owned(), &login_token);
-
-        return Ok((
-            AppendHeaders(vec![(
-                header::SET_COOKIE,
-                utils::reset_cookie("sso-session").to_string(),
-            )]),
-            Redirect::temporary(redirect_uri.as_str()),
-        )
-            .into_response());
-    }
-
-    match provider.config.registration {
-        Registration::Disabled => {
+    let subject = match id_token.get(SUBJECT_CLAIM_KEY) {
+        Some(Value::String(s)) => s.to_owned(),
+        Some(Value::Number(n)) => n.to_string(),
+        value => {
             return Err(Error::BadRequest(
-                ErrorKind::forbidden(),
-                "Single Sign-On registration is disabled.",
-            ))
+                ErrorKind::Unknown,
+                value
+                    .map(|_| {
+                        error!("Subject claim is missing from ID token: {id_token:?}");
+
+                        "Subject claim is missing from ID token."
+                    })
+                    .unwrap_or("Subject claim should be a string or number."),
+            ));
         }
-        Registration::Automated => todo!(),
-        Registration::Interactive => {}
     };
 
-    let Template {
-        username,
-        displayname,
-        avatar_url,
-        email,
-    } = &provider.config.template;
-    let registration_info =
-        RegistrationInfo::new(&claims, username, displayname, avatar_url, email);
-
-    let signed = services()
-        .globals
-        .sign_macaroon(&RegistrationToken::new(
-            validation_data.provider_id.clone(),
-            subject.to_owned(),
-            redirect_uri.to_owned(),
-            registration_info,
-        ))
-        .expect("signing macaroons always works");
-
-    let cookie = utils::build_cookie(
-        "sso-registration",
-        &signed,
-        "/_conduit/client/sso/register",
-        REGISTRATION_EXPIRATION_SECS,
-    );
-
-    Ok((
-        AppendHeaders(vec![
-            (header::SET_COOKIE, cookie.to_string()),
-            (
-                header::SET_COOKIE,
-                utils::reset_cookie("sso-session").to_string(),
-            ),
-        ]),
-        Redirect::temporary("/_conduit/client/sso/register"),
-    )
-        .into_response())
-}
-
-/// # `GET /_conduit/client/sso/pick_idp`
-pub async fn pick_idp(RawQuery(query): RawQuery) -> impl IntoResponse {
-    let providers: Vec<_> = services()
-        .globals
-        .config
+    let user_id = match services()
         .sso
-        .iter()
-        .map(|p| p.inner.to_owned())
-        .collect();
+        .user_from_subject(Borrow::<str>::borrow(provider), &subject)?
+    {
+        Some(user_id) => user_id,
+        None => {
+            let mut localpart = subject.clone();
 
-    let body = maud::html! {
-        header {
-            h1 { "Log in to " (services().globals.server_name()) }
-            p { "Choose an identity provider to continue" }
-        }
-        main {
-            ul .providers {
-                @for provider in providers {
-                    li {
-                        a href={ "/_matrix/client/v3/login/sso/redirect/" (provider.id) "?" (query.as_deref().unwrap_or_default()) } {
-                            @if let Some(url) = provider.icon.as_deref().and_then(utils::mxc_to_http) {
-                                img src=(url);
-                            }
-                        }
-                        span {
-                            (provider.name)
-                        }
+            let user_id = loop {
+                match UserId::parse_with_server_name(&*localpart, services().globals.server_name())
+                {
+                    Ok(user_id) if services().users.exists(&user_id)? => break user_id,
+                    _ => {
+                        let n: u8 = rand::thread_rng().gen();
+
+                        localpart = format!("{}{}", localpart, n % 10);
                     }
                 }
+            };
+
+            services().users.set_placeholder_password(&user_id)?;
+            let mut displayname = id_token
+                .get("preferred_username")
+                .or(id_token.get("nickname"))
+                .as_deref()
+                .map(Value::to_string)
+                .unwrap_or(user_id.localpart().to_owned());
+
+            // If enabled append lightning bolt to display name (default true)
+            if services().globals.enable_lightning_bolt() {
+                displayname.push_str(" ⚡️");
             }
+
+            services()
+                .users
+                .set_displayname(&user_id, Some(displayname.clone()))?;
+
+            // Initial account data
+            services().account_data.update(
+                None,
+                &user_id,
+                GlobalAccountDataEventType::PushRules.to_string().into(),
+                &serde_json::to_value(ruma::events::push_rules::PushRulesEvent {
+                    content: ruma::events::push_rules::PushRulesEventContent {
+                        global: push::Ruleset::server_default(&user_id),
+                    },
+                })
+                .expect("to json always works"),
+            )?;
+
+            info!("New user {} registered on this server.", user_id);
+            services()
+                .admin
+                .send_message(RoomMessageEventContent::notice_plain(format!(
+                    "New user {user_id} registered on this server."
+                )));
+
+            if let Some(admin_room) = services().admin.get_admin_room()? {
+                if services()
+                    .rooms
+                    .state_cache
+                    .room_joined_count(&admin_room)?
+                    == Some(1)
+                {
+                    services()
+                        .admin
+                        .make_user_admin(&user_id, displayname)
+                        .await?;
+
+                    warn!("Granting {} admin privileges as the first user", user_id);
+                }
+            }
+
+            user_id
         }
     };
 
-    (
-        [(header::CONTENT_TYPE, "text/html; charset=utf-8")],
-        maud::html! {
-            (templates::base("Pick Identity Provider", body))
+    let signed = services().globals.sign_claims(&LoginToken::new(
+        Borrow::<str>::borrow(provider).to_owned(),
+        user_id,
+    ));
 
-            (templates::footer())
-        },
-    )
-}
-
-/// # `GET /_conduit/client/sso/register`
-///
-/// Serve a registration form with defaults based on the retrieved claims.
-/// This endpoint is only available when interactive registration is enabled.
-pub async fn get_sso_registration(
-    cookie: TypedHeader<headers::Cookie>,
-) -> Result<axum::response::Response> {
-    let token = cookie.get("sso-registration").ok_or_else(|| {
-        Error::BadRequest(
-            ErrorKind::MissingParam,
-            "Missing registration token cookie.",
-        )
-    })?;
-
-    let registration_token: RegistrationToken = services()
-        .globals
-        .validate_macaroon(token, None)
-        .map_err(|_| {
-        Error::BadRequest(
-            ErrorKind::InvalidParam,
-            "Invalid registration token cookie.",
-        )
-    })?;
-
-    let provider = services()
-        .sso
-        .get(&registration_token.provider_id)
-        .map(|p| p.config.inner.to_owned())?;
-    let server_name = services().globals.server_name();
-
-    let RegistrationInfo {
-        username,
-        displayname,
-        avatar_url,
-        email,
-    } = registration_token.info;
-
-    let additional_info = (&displayname, &avatar_url, &email) != (&None, &None, &None);
-
-    fn detail(title: &str, body: maud::Markup) -> maud::Markup {
-        maud::html! {
-            label .detail for=(title) {
-                div .check-row {
-                    span .name { (title) } " "
-                    span .use { "use" }
-                    input #(title) type="checkbox" name={(title)"-checkbox"} value=(true) checked;
-                }
-                (body)
-            }
-        }
-    }
-
-    let body = maud::html! {
-        header {
-            h1 { "Complete your registration at " (server_name) }
-            p { "Confirm your details to finish creating your account." }
-        }
-        main {
-            form .form #form method="post" {
-                div .username-div #username-div {
-                    label for="username-input" { "Username (required)" }
-                    div .prefix { "@" }
-                    input .username-input type="text" name="username"
-                        value=(username) autofocus autocorrect="off" autocapitalize="none";
-                    div .postfix { ":" (server_name) }
-                }
-                output .username-output for="username-input" { }
-
-                @if additional_info {
-                    section .additional-info {
-                        h2 {
-                            @if let Some(icon) = provider.icon.as_deref().and_then(utils::mxc_to_http) {
-                                img src=(icon.to_string());
-                            }
-                            "Optional data from " (provider.name)
-                        }
-                        @if let Some(avatar_url) = avatar_url.as_ref() {
-                            (detail("avatar", maud::html!{
-                                img .avatar src=(avatar_url);
-                            }))
-                        }
-                        @if let Some(displayname) = displayname.as_ref() {
-                            (detail("displayname", maud::html!{
-                                p .value { (displayname) };
-                            }))
-                        }
-                        @if let Some(email) = email.as_ref() {
-                            (detail("email", maud::html!{
-                                p .value { (email) };
-                            }))
-                        }
-                    }
-                }
-
-                input type="submit" value="Submit" .primary-button {}
-            }
-        }
-    };
+    let mut redirect_uri = validation_data.redirect_uri;
+    redirect_uri
+        .query_pairs_mut()
+        .append_pair("loginToken", &signed);
 
     Ok((
-        [(header::CONTENT_TYPE, "text/html; charset=utf-8")],
-        maud::html! {
-            (templates::base("Register Account", body))
-
-            (templates::footer())
-        },
-    )
-        .into_response())
-}
-
-/// # `POST /_conduit/client/sso/register`
-///
-/// Submit the registration form.
-pub async fn submit_sso_registration(
-    cookie: TypedHeader<headers::Cookie>,
-    axum::extract::Form(registration_info): axum::extract::Form<RegistrationInfo>,
-) -> Result<axum::response::Response> {
-    let token = cookie.get("sso-registration").ok_or_else(|| {
-        Error::BadRequest(
-            ErrorKind::MissingParam,
-            "Missing registration token cookie.",
-        )
-    })?;
-
-    let registration_token: RegistrationToken = services()
-        .globals
-        .validate_macaroon(token, None)
-        .map_err(|_| {
-        Error::BadRequest(
-            ErrorKind::MissingParam,
-            "Invalid registration token cookie.",
-        )
-    })?;
-
-    let RegistrationInfo {
-        username,
-        mut displayname,
-        avatar_url,
-        email: _,
-    } = registration_info;
-
-    let user_id =
-        UserId::parse_with_server_name(username.to_lowercase(), services().globals.server_name())
-            .map_err(|_| Error::BadRequest(ErrorKind::InvalidUsername, "Invalid username."))?;
-
-    if services().users.exists(&user_id)? {
-        return Err(Error::BadRequest(
-            ErrorKind::UserInUse,
-            "Desired UserId is already taken.",
-        ));
-    }
-
-    if services().appservice.is_exclusive_user_id(&user_id).await {
-        return Err(Error::BadRequest(
-            ErrorKind::Exclusive,
-            "Desired UserId reserved by appservice.",
-        ));
-    }
-
-    services().users.create(&user_id, None)?;
-    services().users.set_password_placeholder(&user_id)?;
-
-    if let Some(avatar_url) = avatar_url {
-        let request = services().globals.default_client().get(avatar_url.as_ref());
-
-        let res = request.send().await.map_err(|_| {
-            Error::BadRequest(ErrorKind::UserInUse, "Desired UserId is already taken.")
-        })?;
-
-        let filename = avatar_url.path_segments().and_then(Iterator::last);
-
-        let (content_type, body): (Option<headers::ContentType>, Vec<u8>) = (
-            res.headers().typed_get(),
-            res.bytes().await.map(Into::into).map_err(|_| {
-                Error::BadRequest(ErrorKind::UserInUse, "Desired UserId is already taken.")
-            })?,
-        );
-
-        let mxc = format!(
-            "mxc://{}/{}",
-            services().globals.server_name(),
-            utils::random_string(crate::api::client_server::MXC_LENGTH)
-        );
-
-        services()
-            .media
-            .create(
-                mxc.clone(),
-                filename
-                    .map(|filename| "inline; filename=".to_owned() + filename)
-                    .as_deref(),
-                content_type.map(|header| header.to_string()).as_deref(),
-                &body,
-            )
-            .await?;
-
-        services()
-            .users
-            .set_avatar_url(&user_id, Some(OwnedMxcUri::from(mxc)))?;
-    };
-
-    if let (Some(displayname), true) = (
-        displayname.as_mut(),
-        services().globals.config.enable_lightning_bolt,
-    ) {
-        displayname.push_str(" ⚡️");
-    }
-
-    services().users.set_displayname(&user_id, displayname)?;
-
-    services().sso.save_claim(
-        &registration_token.provider_id,
-        &user_id,
-        &registration_token.unique_claim,
-    )?;
-
-    services().account_data.update(
-        None,
-        &user_id,
-        GlobalAccountDataEventType::PushRules.to_string().into(),
-        &serde_json::to_value(ruma::events::push_rules::PushRulesEvent {
-            content: ruma::events::push_rules::PushRulesEventContent {
-                global: push::Ruleset::server_default(&user_id),
-            },
-        })
-        .expect("PushRulesEvent should always serialize"),
-    )?;
-
-    let login_token = LoginToken::new(registration_token.provider_id, user_id);
-    let redirect_uri = redirect_with_login_token(registration_token.redirect_uri, &login_token);
-
-    Ok((
-        AppendHeaders([(
+        AppendHeaders(vec![(
             header::SET_COOKIE,
-            utils::reset_cookie("sso-registration").to_string(),
+            utils::build_cookie(SSO_SESSION_COOKIE, "", CALLBACK_PATH, None).to_string(),
         )]),
         Redirect::temporary(redirect_uri.as_str()),
     )
         .into_response())
 }
 
-fn redirect_with_login_token(mut redirect_uri: Url, login_token: &LoginToken) -> Url {
-    let signed = services()
-        .globals
-        .sign_macaroon(login_token)
-        .expect("signing macaroons should always works");
-
-    redirect_uri
-        .query_pairs_mut()
-        .append_pair("loginToken", &signed);
-
-    redirect_uri
+/// # `GET /_conduit/client/sso/callback`
+///
+/// Validate the authorization response received from the identity provider.
+/// On success, generate a login token, add it to `redirectUrl` as a query and perform the redirect.
+/// If this is the first login, register the user, possibly interactively through a fallback page.
+pub async fn handle_callback_route(req: axum::extract::Request) -> axum::response::Response {
+    match handle_callback_helper(req).await {
+        Ok(res) => res,
+        Err(e) => e.into_response(),
+    }
 }
diff --git a/src/database/key_value/sso.rs b/src/database/key_value/sso.rs
new file mode 100644
index 00000000..1f6eab28
--- /dev/null
+++ b/src/database/key_value/sso.rs
@@ -0,0 +1,29 @@
+use ruma::{OwnedUserId, UserId};
+
+use crate::{service, utils, Error, KeyValueDatabase, Result};
+
+impl service::sso::Data for KeyValueDatabase {
+    fn save_subject(&self, provider: &str, user_id: &UserId, subject: &str) -> Result<()> {
+        let mut key = provider.as_bytes().to_vec();
+        key.push(0xff);
+        key.extend_from_slice(subject.as_bytes());
+
+        self.subject_userid.insert(&key, user_id.as_bytes())
+    }
+
+    fn user_from_subject(&self, provider: &str, subject: &str) -> Result<Option<OwnedUserId>> {
+        let mut key = provider.as_bytes().to_vec();
+        key.push(0xff);
+        key.extend_from_slice(subject.as_bytes());
+
+        self.subject_userid.get(&key)?.map_or(Ok(None), |bytes| {
+            Some(
+                UserId::parse(utils::string_from_bytes(&bytes).map_err(|_| {
+                    Error::bad_database("User ID in claim_userid is invalid unicode.")
+                })?)
+                .map_err(|_| Error::bad_database("User ID in claim_userid is invalid.")),
+            )
+            .transpose()
+        })
+    }
+}
diff --git a/src/database/mod.rs b/src/database/mod.rs
index 16a5e60a..39550a93 100644
--- a/src/database/mod.rs
+++ b/src/database/mod.rs
@@ -49,6 +49,7 @@ pub struct KeyValueDatabase {
     pub(super) userdeviceid_metadata: Arc<dyn KvTree>, // This is also used to check if a device exists
     pub(super) userid_devicelistversion: Arc<dyn KvTree>, // DevicelistVersion = u64
     pub(super) token_userdeviceid: Arc<dyn KvTree>,
+    pub(super) subject_userid: Arc<dyn KvTree>,
 
     pub(super) onetimekeyid_onetimekeys: Arc<dyn KvTree>, // OneTimeKeyId = UserId + DeviceKeyId
     pub(super) userid_lastonetimekeyupdate: Arc<dyn KvTree>, // LastOneTimeKeyUpdate = Count
@@ -289,6 +290,8 @@ impl KeyValueDatabase {
             userdeviceid_metadata: builder.open_tree("userdeviceid_metadata")?,
             userid_devicelistversion: builder.open_tree("userid_devicelistversion")?,
             token_userdeviceid: builder.open_tree("token_userdeviceid")?,
+            subject_userid: builder.open_tree("subject_userid")?,
+
             onetimekeyid_onetimekeys: builder.open_tree("onetimekeyid_onetimekeys")?,
             userid_lastonetimekeyupdate: builder.open_tree("userid_lastonetimekeyupdate")?,
             keychangeid_userid: builder.open_tree("keychangeid_userid")?,
diff --git a/src/main.rs b/src/main.rs
index 0b07fe2b..c3ad4c1e 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -10,7 +10,7 @@ use axum::{
 };
 use axum_server::{bind, bind_rustls, tls_rustls::RustlsConfig, Handle as ServerHandle};
 use conduit::api::{
-    client_server::{self, SSO_CALLBACK_PATH},
+    client_server::{self, CALLBACK_PATH},
     server_server,
 };
 use figment::{
@@ -283,7 +283,7 @@ fn routes(config: &Config) -> Router {
         .ruma_route(client_server::get_sso_redirect_with_provider_route)
         // The specification will likely never introduce any endpoint for handling authorization callbacks.
         // As a workaround, we use custom path that redirects the user to the default login handler.
-        .route(SSO_CALLBACK_PATH, get(client_server::sso_login_route))
+        .route(CALLBACK_PATH, get(client_server::handle_callback_route))
         .ruma_route(client_server::get_capabilities_route)
         .ruma_route(client_server::get_pushrules_all_route)
         .ruma_route(client_server::set_pushrule_route)
diff --git a/src/service/mod.rs b/src/service/mod.rs
index fae5a726..6d8c34d2 100644
--- a/src/service/mod.rs
+++ b/src/service/mod.rs
@@ -123,7 +123,7 @@ impl Services {
             key_backups: key_backups::Service { db },
             media: media::Service { db },
             sending: sending::Service::build(db, &config),
-            sso: sso::Service::build(db),
+            sso: sso::Service::build(db)?,
 
             globals: globals::Service::load(db, config)?,
         })
diff --git a/src/service/sso/mod.rs b/src/service/sso/mod.rs
index 1206ed34..31c9c3ab 100644
--- a/src/service/sso/mod.rs
+++ b/src/service/sso/mod.rs
@@ -1,50 +1,36 @@
-mod data;
 use std::{
     borrow::Borrow,
-    collections::{HashMap, HashSet},
+    collections::HashSet,
     hash::{Hash, Hasher},
-    str::FromStr,
-    sync::{Arc, RwLock},
-    time::{Duration, SystemTime, UNIX_EPOCH},
+    sync::Arc,
 };
 
 use crate::{
-    api::client_server::TOKEN_LENGTH,
-    config::{sso::ProviderConfig as Config, IdpConfig},
+    api::client_server::{LOGIN_TOKEN_EXPIRATION_SECS, TOKEN_LENGTH},
+    config::IdpConfig,
     utils, Error, Result,
 };
-pub use data::Data;
-use email_address::EmailAddress;
 use futures_util::future::{self};
 use mas_oidc_client::{
     http_service::{hyper, HttpService},
-    jose::jwk::PublicJsonWebKeySet,
-    requests::{
-        authorization_code::{self, AuthorizationRequestData, AuthorizationValidationData},
-        discovery,
-        jose::{self, JwtVerificationData},
-        userinfo,
-    },
-    types::{
-        iana::jose::JsonWebSignatureAlg, oidc::VerifiedProviderMetadata,
-        requests::AccessTokenResponse, IdToken,
-    },
+    requests::{authorization_code::AuthorizationValidationData, discovery},
+    types::oidc::VerifiedProviderMetadata,
 };
-use rand::SeedableRng;
-use ruma::{api::client::error::ErrorKind, MilliSecondsSinceUnixEpoch, OwnedUserId, UserId};
+use ruma::{api::client::session::get_login_types::v3::IdentityProvider, OwnedUserId, UserId};
 use serde::{Deserialize, Serialize};
-use serde_json::Value;
-use tokio::sync::{oneshot, OnceCell};
+use tokio::sync::OnceCell;
 use tracing::error;
 use url::Url;
 
 use crate::services;
 
+mod data;
 pub use data::Data;
 
 pub const SSO_AUTH_EXPIRATION_SECS: u64 = 60 * 60;
 pub const SSO_TOKEN_EXPIRATION_SECS: u64 = 60 * 2;
 pub const SSO_SESSION_COOKIE: &str = "sso-auth";
+pub const SUBJECT_CLAIM_KEY: &str = "sub";
 
 pub struct Service {
     db: &'static dyn Data,
@@ -69,7 +55,7 @@ impl Service {
         let providers = services().globals.config.idps.iter();
 
         self.providers
-            .get_or_try_init(|| {
+            .get_or_try_init(|| async move {
                 future::try_join_all(providers.map(Provider::fetch_metadata))
                     .await
                     .map(Vec::into_iter)
@@ -86,6 +72,12 @@ impl Service {
         providers.get(provider)
     }
 
+    pub fn login_type(&self) -> impl Iterator<Item = IdentityProvider> + '_ {
+        let providers = self.providers.get().expect("");
+
+        providers.iter().map(|p| p.config.inner.clone())
+    }
+
     pub fn user_from_subject(&self, provider: &str, subject: &str) -> Result<Option<OwnedUserId>> {
         self.db.user_from_subject(provider, subject)
     }
@@ -111,30 +103,6 @@ impl Provider {
                 Error::bad_config("Failed to fetch identity provider metadata.")
             })
     }
-
-    async fn fetch_signing_keys(&self) -> Result<PublicJsonWebKeySet> {
-        jose::fetch_jwks(&services().sso.service, self.metadata.jwks_uri())
-            .await
-            .map_err(|e| {
-                error!("Failed to fetch signing keys for token endpoint: {}", e);
-
-                Error::bad_config("Failed to fetch signing keys for token endpoint.")
-            })
-    }
-
-    pub async fn fetch_access_token(
-        &self,
-        auth_code: String,
-        validation_data: AuthorizationValidationData,
-    ) -> Result<(AccessTokenResponse, Option<IdToken<'_>>)> {
-    }
-
-    pub async fn fetch_userinfo(
-        &self,
-        access_token: &str,
-        id_token: &IdToken<'_>,
-    ) -> Result<Option<HashMap<String, Value>>> {
-    }
 }
 
 impl Borrow<str> for Provider {
@@ -157,105 +125,28 @@ impl Hash for Provider {
     }
 }
 
-#[derive(Clone, Debug, Deserialize, Serialize)]
-pub struct RegistrationToken {
-    pub info: RegistrationInfo,
-    pub provider_id: String,
-    pub unique_claim: String,
-    pub redirect_uri: Url,
-    pub expires_at: MilliSecondsSinceUnixEpoch,
-}
-
-impl RegistrationToken {
-    pub fn new(
-        provider_id: String,
-        unique_claim: String,
-        redirect_uri: Url,
-        info: RegistrationInfo,
-    ) -> Self {
-        let expires_at = MilliSecondsSinceUnixEpoch::from_system_time(
-            UNIX_EPOCH
-                .checked_add(Duration::from_secs(REGISTRATION_EXPIRATION_SECS))
-                .expect("SystemTime should not overflow"),
-        )
-        .expect("MilliSecondsSinceUnixEpoch is not too large");
-
-        Self {
-            info,
-            provider_id,
-            unique_claim,
-            redirect_uri,
-            expires_at,
-        }
-    }
-}
-
-#[derive(Clone, Debug, Default, Deserialize, Serialize)]
-pub struct RegistrationInfo {
-    pub username: String,
-    pub displayname: Option<String>,
-    pub avatar_url: Option<Url>,
-    pub email: Option<EmailAddress>,
-}
-
-impl RegistrationInfo {
-    pub fn new(
-        claims: &HashMap<String, Value>,
-        username: &str,
-        displayname: &str,
-        avatar_url: &str,
-        email: &str,
-    ) -> Self {
-        Self {
-            username: claims
-                .get(username)
-                .and_then(|v| v.as_str())
-                .map(ToOwned::to_owned)
-                .unwrap_or_default(),
-            displayname: claims
-                .get(displayname)
-                .and_then(|v| v.as_str())
-                .map(ToOwned::to_owned),
-            avatar_url: claims
-                .get(avatar_url)
-                .and_then(|v| v.as_str())
-                .map(Url::parse)
-                .and_then(Result::ok),
-            email: claims
-                .get(email)
-                .and_then(|v| v.as_str())
-                .map(EmailAddress::from_str)
-                .and_then(Result::ok),
-        }
-    }
-}
-
 #[derive(Clone, Deserialize, Serialize)]
 pub struct LoginToken {
-    pub inner: String,
-    pub provider_id: String,
-    pub user_id: OwnedUserId,
-
-    #[serde(rename = "exp")]
-    expires_at: u64,
+    pub iss: String,
+    pub aud: OwnedUserId,
+    pub sub: String,
+    pub exp: u64,
 }
 
 impl LoginToken {
-    pub fn new(provider_id: String, user_id: OwnedUserId) -> Self {
-        let expires_at = SystemTime::now()
-            .checked_add(Duration::from_secs(LOGIN_TOKEN_EXPIRATION_SECS))
-            .expect("SystemTime should not overflow")
-            .duration_since(UNIX_EPOCH)
-            .expect("SystemTime went backwards")
-            .as_secs();
-
+    pub fn new(provider: String, user_id: OwnedUserId) -> Self {
         Self {
-            inner: utils::random_string(TOKEN_LENGTH),
-            provider_id,
-            user_id,
-            expires_at,
+            iss: provider,
+            aud: user_id,
+            sub: utils::random_string(TOKEN_LENGTH),
+            exp: utils::millis_since_unix_epoch()
+                .checked_add(LOGIN_TOKEN_EXPIRATION_SECS * 1000)
+                .expect("time overflow"),
         }
     }
+    pub fn audience(&self) -> &UserId {
+        &self.aud
+    }
 }
 
 #[derive(Clone, Debug, Deserialize, Serialize)]