Basic Webfinger support

crates/handlers/src/lib.rs

@@ -61,6 +61,7 @@ where
             "/.well-known/openid-configuration",
             get(self::oauth2::discovery::get),
         )
+        .route("/.well-known/webfinger", get(self::oauth2::webfinger::get))
         .route("/oauth2/keys.json", get(self::oauth2::keys::get))
         .route(
             "/oauth2/userinfo",

crates/handlers/src/oauth2/mod.rs

@@ -18,5 +18,6 @@ pub mod introspection;
 pub mod keys;
 pub mod token;
 pub mod userinfo;
+pub mod webfinger;
 
 pub(crate) use authorization::ContinueAuthorizationGrant;

crates/handlers/src/oauth2/webfinger.rs

@@ -0,0 +1,53 @@
+// Copyright 2022 The Matrix.org Foundation C.I.C.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+use axum::{extract::Query, response::IntoResponse, Extension, Json, TypedHeader};
+use headers::ContentType;
+use mas_axum_utils::UrlBuilder;
+use oauth2_types::webfinger::WebFingerResponse;
+use serde::Deserialize;
+
+#[derive(Deserialize)]
+pub(crate) struct Params {
+    resource: String,
+
+    // TODO: handle multiple rel=
+    #[serde(default)]
+    rel: Option<String>,
+}
+
+fn jrd() -> mime::Mime {
+    "application/jrd+json".parse().unwrap()
+}
+
+pub(crate) async fn get(
+    Query(params): Query<Params>,
+    Extension(url_builder): Extension<UrlBuilder>,
+) -> impl IntoResponse {
+    // TODO: should we validate the subject?
+    let subject = params.resource;
+
+    let wants_issuer = params
+        .rel
+        .iter()
+        .any(|i| i == "http://openid.net/specs/connect/1.0/issuer");
+
+    let res = if wants_issuer {
+        WebFingerResponse::new(subject).with_issuer(url_builder.oidc_issuer())
+    } else {
+        WebFingerResponse::new(subject)
+    };
+
+    (TypedHeader(ContentType::from(jrd())), Json(res))
+}