Allow the homeserver to perform introspection using a shared secret

Author: sandhose

crates/axum-utils/src/client_authorization.rs

@@ -9,13 +9,12 @@ use std::collections::HashMap;
 use axum::{
     BoxError, Json,
     extract::{
-        Form, FromRequest, FromRequestParts,
+        Form, FromRequest,
         rejection::{FailedToDeserializeForm, FormRejection},
     },
     response::IntoResponse,
 };
-use axum_extra::typed_header::{TypedHeader, TypedHeaderRejectionReason};
-use headers::{Authorization, authorization::Basic};
+use headers::authorization::{Basic, Bearer, Credentials as _};
 use http::{Request, StatusCode};
 use mas_data_model::{Client, JwksOrJwksUri};
 use mas_http::RequestBuilderExt;
@@ -60,17 +59,30 @@ pub enum Credentials {
         client_id: String,
         jwt: Box<Jwt<'static, HashMap<String, serde_json::Value>>>,
     },
+    BearerToken {
+        token: String,
+    },
 }
 
 impl Credentials {
     /// Get the `client_id` of the credentials
     #[must_use]
-    pub fn client_id(&self) -> &str {
+    pub fn client_id(&self) -> Option<&str> {
         match self {
             Credentials::None { client_id }
             | Credentials::ClientSecretBasic { client_id, .. }
             | Credentials::ClientSecretPost { client_id, .. }
-            | Credentials::ClientAssertionJwtBearer { client_id, .. } => client_id,
+            | Credentials::ClientAssertionJwtBearer { client_id, .. } => Some(client_id),
+            Credentials::BearerToken { .. } => None,
+        }
+    }
+
+    /// Get the bearer token from the credentials.
+    #[must_use]
+    pub fn bearer_token(&self) -> Option<&str> {
+        match self {
+            Credentials::BearerToken { token } => Some(token),
+            _ => None,
         }
     }
 
@@ -89,6 +101,7 @@ impl Credentials {
             | Credentials::ClientSecretBasic { client_id, .. }
             | Credentials::ClientSecretPost { client_id, .. }
             | Credentials::ClientAssertionJwtBearer { client_id, .. } => client_id,
+            Credentials::BearerToken { .. } => return Ok(None),
         };
 
         repo.oauth2_client().find_by_client_id(client_id).await
@@ -239,7 +252,7 @@ pub struct ClientAuthorization<F = ()> {
 impl<F> ClientAuthorization<F> {
     /// Get the `client_id` from the credentials.
     #[must_use]
-    pub fn client_id(&self) -> &str {
+    pub fn client_id(&self) -> Option<&str> {
         self.credentials.client_id()
     }
 }
@@ -360,25 +373,36 @@ where
         req: Request<axum::body::Body>,
         state: &S,
     ) -> Result<Self, Self::Rejection> {
-        // Split the request into parts so we can extract some headers
-        let (mut parts, body) = req.into_parts();
-
-        let header =
-            TypedHeader::<Authorization<Basic>>::from_request_parts(&mut parts, state).await;
-
-        // Take the Authorization header
-        let credentials_from_header = match header {
-            Ok(header) => Some((header.username().to_owned(), header.password().to_owned())),
-            Err(err) => match err.reason() {
-                // If it's missing it is fine
-                TypedHeaderRejectionReason::Missing => None,
-                // If the header could not be parsed, return the error
-                _ => return Err(ClientAuthorizationError::InvalidHeader),
-            },
-        };
+        enum Authorization {
+            Basic(String, String),
+            Bearer(String),
+        }
+
+        // Sadly, the typed-header 'Authorization' doesn't let us check for both
+        // Basic and Bearer at the same time, so we need to parse them manually
+        let authorization = if let Some(header) = req.headers().get(http::header::AUTHORIZATION) {
+            let bytes = header.as_bytes();
+            if bytes.len() >= 6 && bytes[..6].eq_ignore_ascii_case(b"Basic ") {
+                let Some(decoded) = Basic::decode(header) else {
+                    return Err(ClientAuthorizationError::InvalidHeader);
+                };
 
-        // Reconstruct the request from the parts
-        let req = Request::from_parts(parts, body);
+                Some(Authorization::Basic(
+                    decoded.username().to_owned(),
+                    decoded.password().to_owned(),
+                ))
+            } else if bytes.len() >= 7 && bytes[..7].eq_ignore_ascii_case(b"Bearer ") {
+                let Some(decoded) = Bearer::decode(header) else {
+                    return Err(ClientAuthorizationError::InvalidHeader);
+                };
+
+                Some(Authorization::Bearer(decoded.token().to_owned()))
+            } else {
+                return Err(ClientAuthorizationError::InvalidHeader);
+            }
+        } else {
+            None
+        };
 
         // Take the form value
         let (
@@ -407,13 +431,19 @@ where
 
         // And now, figure out the actual auth method
         let credentials = match (
-            credentials_from_header,
+            authorization,
             client_id_from_form,
             client_secret_from_form,
             client_assertion_type,
             client_assertion,
         ) {
-            (Some((client_id, client_secret)), client_id_from_form, None, None, None) => {
+            (
+                Some(Authorization::Basic(client_id, client_secret)),
+                client_id_from_form,
+                None,
+                None,
+                None,
+            ) => {
                 if let Some(client_id_from_form) = client_id_from_form {
                     // If the client_id was in the body, verify it matches with the header
                     if client_id != client_id_from_form {
@@ -483,6 +513,11 @@ where
                 });
             }
 
+            (Some(Authorization::Bearer(token)), None, None, None, None) => {
+                // Got a bearer token
+                Credentials::BearerToken { token }
+            }
+
             (None, None, None, None, None) => {
                 // Special case when there are no credentials anywhere
                 return Err(ClientAuthorizationError::MissingCredentials);
@@ -677,4 +712,29 @@ mod tests {
         jwt.verify_with_shared_secret(b"client-secret".to_vec())
             .unwrap();
     }
+
+    #[tokio::test]
+    async fn bearer_token_test() {
+        let req = Request::builder()
+            .method(Method::POST)
+            .header(
+                http::header::CONTENT_TYPE,
+                mime::APPLICATION_WWW_FORM_URLENCODED.as_ref(),
+            )
+            .header(http::header::AUTHORIZATION, "Bearer token")
+            .body(Body::new("foo=bar".to_owned()))
+            .unwrap();
+
+        assert_eq!(
+            ClientAuthorization::<serde_json::Value>::from_request(req, &())
+                .await
+                .unwrap(),
+            ClientAuthorization {
+                credentials: Credentials::BearerToken {
+                    token: "token".to_owned(),
+                },
+                form: Some(serde_json::json!({"foo": "bar"})),
+            }
+        );
+    }
 }

crates/handlers/src/oauth2/introspection.rs

@@ -4,7 +4,7 @@
 // SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
 // Please see LICENSE files in the repository root for full details.
 
-use std::sync::LazyLock;
+use std::sync::{Arc, LazyLock};
 
 use axum::{Json, extract::State, http::HeaderValue, response::IntoResponse};
 use hyper::{HeaderMap, StatusCode};
@@ -15,6 +15,7 @@ use mas_axum_utils::{
 use mas_data_model::{Device, TokenFormatError, TokenType};
 use mas_iana::oauth::{OAuthClientAuthenticationMethod, OAuthTokenTypeHint};
 use mas_keystore::Encrypter;
+use mas_matrix::HomeserverConnection;
 use mas_storage::{
     BoxClock, BoxRepository, Clock,
     compat::{CompatAccessTokenRepository, CompatRefreshTokenRepository, CompatSessionRepository},
@@ -102,8 +103,14 @@ pub enum RouteError {
     #[error("bad request")]
     BadRequest,
 
+    #[error("failed to verify token")]
+    FailedToVerifyToken(#[source] anyhow::Error),
+
     #[error(transparent)]
     ClientCredentialsVerification(#[from] CredentialsVerificationError),
+
+    #[error("bearer token presented is invalid")]
+    InvalidBearerToken,
 }
 
 impl IntoResponse for RouteError {
@@ -114,13 +121,15 @@ impl IntoResponse for RouteError {
                 | Self::CantLoadCompatSession(_)
                 | Self::CantLoadOAuthSession(_)
                 | Self::CantLoadUser(_)
+                | Self::FailedToVerifyToken(_)
         );
 
         let response = match self {
             e @ (Self::Internal(_)
             | Self::CantLoadCompatSession(_)
             | Self::CantLoadOAuthSession(_)
-            | Self::CantLoadUser(_)) => (
+            | Self::CantLoadUser(_)
+            | Self::FailedToVerifyToken(_)) => (
                 StatusCode::INTERNAL_SERVER_ERROR,
                 Json(
                     ClientError::from(ClientErrorCode::ServerError).with_description(e.to_string()),
@@ -140,6 +149,14 @@ impl IntoResponse for RouteError {
                 ),
             )
                 .into_response(),
+            e @ Self::InvalidBearerToken => (
+                StatusCode::UNAUTHORIZED,
+                Json(
+                    ClientError::from(ClientErrorCode::AccessDenied)
+                        .with_description(e.to_string()),
+                ),
+            )
+                .into_response(),
 
             Self::UnknownToken(_)
             | Self::UnexpectedTokenType
@@ -195,7 +212,7 @@ const SYNAPSE_ADMIN_SCOPE: ScopeToken = ScopeToken::from_static("urn:synapse:adm
 
 #[tracing::instrument(
     name = "handlers.oauth2.introspection.post",
-    fields(client.id = client_authorization.client_id()),
+    fields(client.id = credentials.client_id()),
     skip_all,
 )]
 #[allow(clippy::too_many_lines)]
@@ -205,28 +222,41 @@ pub(crate) async fn post(
     mut repo: BoxRepository,
     activity_tracker: ActivityTracker,
     State(encrypter): State<Encrypter>,
+    State(homeserver): State<Arc<dyn HomeserverConnection>>,
     headers: HeaderMap,
-    client_authorization: ClientAuthorization<IntrospectionRequest>,
+    ClientAuthorization { credentials, form }: ClientAuthorization<IntrospectionRequest>,
 ) -> Result<impl IntoResponse, RouteError> {
-    let client = client_authorization
-        .credentials
-        .fetch(&mut repo)
-        .await?
-        .ok_or(RouteError::ClientNotFound)?;
-
-    let method = match &client.token_endpoint_auth_method {
-        None | Some(OAuthClientAuthenticationMethod::None) => {
-            return Err(RouteError::NotAllowed(client.id));
+    if let Some(token) = credentials.bearer_token() {
+        // If the client presented a bearer token, we check with the homeserver
+        // connection if it is allowed to use the introspection endpoint
+        if !homeserver
+            .verify_token(token)
+            .await
+            .map_err(RouteError::FailedToVerifyToken)?
+        {
+            return Err(RouteError::InvalidBearerToken);
         }
-        Some(c) => c,
-    };
+    } else {
+        // Otherwise, it presented regular client credentials, so we verify them
+        let client = credentials
+            .fetch(&mut repo)
+            .await?
+            .ok_or(RouteError::ClientNotFound)?;
+
+        // Only confidential clients are allowed to introspect
+        let method = match &client.token_endpoint_auth_method {
+            None | Some(OAuthClientAuthenticationMethod::None) => {
+                return Err(RouteError::NotAllowed(client.id));
+            }
+            Some(c) => c,
+        };
 
-    client_authorization
-        .credentials
-        .verify(&http_client, &encrypter, method, &client)
-        .await?;
+        credentials
+            .verify(&http_client, &encrypter, method, &client)
+            .await?;
+    }
 
-    let Some(form) = client_authorization.form else {
+    let Some(form) = form else {
         return Err(RouteError::BadRequest);
     };
 
@@ -578,10 +608,11 @@ mod tests {
     use hyper::{Request, StatusCode};
     use mas_data_model::{AccessToken, RefreshToken};
     use mas_iana::oauth::OAuthTokenTypeHint;
-    use mas_matrix::{HomeserverConnection, ProvisionRequest};
+    use mas_matrix::{HomeserverConnection, MockHomeserverConnection, ProvisionRequest};
     use mas_router::{OAuth2Introspection, OAuth2RegistrationEndpoint, SimpleRoute};
     use mas_storage::Clock;
     use oauth2_types::{
+        errors::{ClientError, ClientErrorCode},
         registration::ClientRegistrationResponse,
         requests::IntrospectionResponse,
         scope::{OPENID, Scope},
@@ -984,4 +1015,29 @@ mod tests {
         let response: IntrospectionResponse = response.json();
         assert!(response.active);
     }
+
+    #[sqlx::test(migrator = "mas_storage_pg::MIGRATOR")]
+    async fn test_introspect_with_bearer_token(pool: PgPool) {
+        setup();
+        let state = TestState::from_pool(pool).await.unwrap();
+
+        // Check that talking to the introspection endpoint with the bearer token from
+        // the MockHomeserverConnection doens't error out
+        let request = Request::post(OAuth2Introspection::PATH)
+            .bearer(MockHomeserverConnection::VALID_BEARER_TOKEN)
+            .form(json!({ "token": "some_token" }));
+        let response = state.request(request).await;
+        response.assert_status(StatusCode::OK);
+        let response: IntrospectionResponse = response.json();
+        assert!(!response.active);
+
+        // Check with another token, we should get a 401
+        let request = Request::post(OAuth2Introspection::PATH)
+            .bearer("another_token")
+            .form(json!({ "token": "some_token" }));
+        let response = state.request(request).await;
+        response.assert_status(StatusCode::UNAUTHORIZED);
+        let response: ClientError = response.json();
+        assert_eq!(response.error, ClientErrorCode::AccessDenied);
+    }
 }

crates/matrix-synapse/src/legacy.rs

@@ -160,6 +160,11 @@ impl HomeserverConnection for SynapseConnection {
         &self.homeserver
     }
 
+    #[tracing::instrument(name = "homeserver.verify_token", skip_all, err(Debug))]
+    async fn verify_token(&self, token: &str) -> Result<bool, anyhow::Error> {
+        Ok(self.access_token == token)
+    }
+
     #[tracing::instrument(
         name = "homeserver.query_user",
         skip_all,

crates/matrix-synapse/src/modern.rs

@@ -66,6 +66,11 @@ impl HomeserverConnection for SynapseConnection {
         &self.homeserver
     }
 
+    #[tracing::instrument(name = "homeserver.verify_token", skip_all, err(Debug))]
+    async fn verify_token(&self, token: &str) -> Result<bool, anyhow::Error> {
+        Ok(self.access_token == token)
+    }
+
     #[tracing::instrument(
         name = "homeserver.query_user",
         skip_all,