Return reason for invalid_client_metadata in HTTP response (#298)

crates/handlers/src/oauth2/registration.rs

@@ -17,7 +17,7 @@ use std::sync::Arc;
 use axum::{response::IntoResponse, Extension, Json};
 use hyper::StatusCode;
 use mas_iana::oauth::{OAuthAuthorizationEndpointResponseType, OAuthClientAuthenticationMethod};
-use mas_policy::PolicyFactory;
+use mas_policy::{PolicyFactory, Violation};
 use mas_storage::oauth2::client::insert_client;
 use oauth2_types::{
     errors::{INVALID_CLIENT_METADATA, INVALID_REDIRECT_URI, SERVER_ERROR},
@@ -44,7 +44,7 @@ pub(crate) enum RouteError {
     InvalidClientMetadata,
 
     #[error("denied by the policy")]
-    PolicyDenied,
+    PolicyDenied(Vec<Violation>),
 }
 
 impl From<sqlx::Error> for RouteError {
@@ -53,17 +53,53 @@ impl From<sqlx::Error> for RouteError {
     }
 }
 
+// TODO: there is probably a better way to do achieve this. ClientError only
+// works for static strings
+#[derive(serde::Serialize)]
+struct PolicyError {
+    error: String,
+    error_description: String,
+}
+
+impl PolicyError {
+    #[must_use]
+    pub const fn new(error: String, error_description: String) -> Self {
+        Self {
+            error,
+            error_description,
+        }
+    }
+}
+
 impl IntoResponse for RouteError {
     fn into_response(self) -> axum::response::Response {
         match self {
             Self::Internal(_) | Self::Anyhow(_) => {
-                (StatusCode::INTERNAL_SERVER_ERROR, Json(SERVER_ERROR))
+                (StatusCode::INTERNAL_SERVER_ERROR, Json(SERVER_ERROR)).into_response()
+            }
+            Self::InvalidRedirectUri => {
+                (StatusCode::BAD_REQUEST, Json(INVALID_REDIRECT_URI)).into_response()
+            }
+            Self::InvalidClientMetadata => {
+                (StatusCode::BAD_REQUEST, Json(INVALID_CLIENT_METADATA)).into_response()
+            }
+            Self::PolicyDenied(violations) => {
+                let collected = &violations
+                    .iter()
+                    .map(|v| v.msg.clone())
+                    .collect::<Vec<String>>();
+                let joined = collected.join("; ");
+
+                (
+                    StatusCode::UNAUTHORIZED,
+                    Json(PolicyError::new(
+                        "invalid_client_metadata".to_string(),
+                        joined,
+                    )),
+                )
+                    .into_response()
             }
-            Self::InvalidRedirectUri => (StatusCode::BAD_REQUEST, Json(INVALID_REDIRECT_URI)),
-            Self::InvalidClientMetadata => (StatusCode::BAD_REQUEST, Json(INVALID_CLIENT_METADATA)),
-            Self::PolicyDenied => (StatusCode::UNAUTHORIZED, Json(INVALID_CLIENT_METADATA)),
         }
-        .into_response()
     }
 }
 
@@ -121,7 +157,7 @@ pub(crate) async fn post(
     let mut policy = policy_factory.instantiate().await?;
     let res = policy.evaluate_client_registration(&body).await?;
     if !res.valid() {
-        return Err(RouteError::PolicyDenied);
+        return Err(RouteError::PolicyDenied(res.violations));
     }
 
     // Grab a txn