identity-service-api: Add public key retrieval endpoint

ruma-identity-service-api/src/keys.rs

@@ -1,3 +1,4 @@
 //! Endpoints to retrieve, update, and validate keys with an identity server.
 
 pub mod check_public_key_validity;
+pub mod get_public_key;

ruma-identity-service-api/src/keys/get_public_key.rs

@@ -0,0 +1,3 @@
+//! Endpoint to retrieve the public key for a key ID.
+
+pub mod v2;

ruma-identity-service-api/src/keys/get_public_key/v2.rs

@@ -0,0 +1,40 @@
+//! [GET /_matrix/identity/v2/pubkey/{keyId}](https://matrix.org/docs/spec/identity_service/r0.3.0#get-matrix-identity-v2-pubkey-keyid)
+
+use ruma_api::ruma_api;
+use ruma_identifiers::ServerSigningKeyId;
+
+ruma_api! {
+    metadata: {
+        description: "Get the public key for the given key ID.",
+        method: GET,
+        name: "get_public_key",
+        path: "/_matrix/identity/v2/pubkey/:key_id",
+        rate_limited: false,
+        authentication: None,
+    }
+
+    request: {
+        /// The ID of the key.
+        #[ruma_api(path)]
+        pub key_id: ServerSigningKeyId,
+    }
+
+    response: {
+        /// Unpadded Base64 encoded public key.
+        pub public_key: String,
+    }
+}
+
+impl Request {
+    /// Create a `Request` with the given key_id.
+    pub fn new(key_id: ServerSigningKeyId) -> Self {
+        Self { key_id }
+    }
+}
+
+impl Response {
+    /// Create a `Response` with the given base64-encoded (unpadded) public key.
+    pub fn new(public_key: String) -> Self {
+        Self { public_key }
+    }
+}