JWT response wrapper

Helps replying with a JWT to a request, with a
`Content-Type: application/jwt` header

crates/axum-utils/src/jwt.rs

@@ -0,0 +1,31 @@
+// 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::{
+    response::{IntoResponse, Response},
+    TypedHeader,
+};
+use headers::ContentType;
+use mas_jose::jwt::Jwt;
+use mime::Mime;
+
+pub struct JwtResponse<T>(pub Jwt<'static, T>);
+
+impl<T> IntoResponse for JwtResponse<T> {
+    fn into_response(self) -> Response {
+        let application_jwt: Mime = "application/jwt".parse().unwrap();
+        let content_type = ContentType::from(application_jwt);
+        (TypedHeader(content_type), self.0.into_string()).into_response()
+    }
+}