Split the registration request model from the registered-client record (#3181)

tests/interaction/_requirements.py

@@ -2940,6 +2940,17 @@ REQUIREMENTS: dict[str, Requirement] = {
         transports=("streamable-http",),
         note="Auth is enforced at the HTTP layer; Cache-Control is an HTTP header.",
     ),
+    "hosting:auth:as:register-echo": Requirement(
+        source="sdk",
+        behavior=(
+            "The bundled registration endpoint returns all registered metadata about the client "
+            "in its 201 response (RFC 7591 §3.2.1) - the client's `application_type` rather than a "
+            "substituted default, and `client_secret_expires_at` (0 when the secret never expires) "
+            "whenever a `client_secret` is issued."
+        ),
+        transports=("streamable-http",),
+        note="Auth is enforced at the HTTP layer; the bundled AS is an ASGI app.",
+    ),
     "hosting:auth:as:register-error-response": Requirement(
         source="sdk",
         behavior=(
@@ -3660,6 +3671,19 @@ REQUIREMENTS: dict[str, Requirement] = {
         transports=("streamable-http",),
         note="OAuth is HTTP-only.",
     ),
+    "client-auth:dcr:substituted-metadata": Requirement(
+        source="sdk",
+        behavior=(
+            "A 201 registration response whose echoed metadata the server substituted (RFC 7591 §3.2.1) - "
+            "an unregistered application_type, null redirect_uris, extra grant types - completes the flow; "
+            "substituted credentials the authorization-code flow cannot apply (an unimplemented "
+            "token_endpoint_auth_method; private_key_jwt, whose assertion it has no key to sign; or a "
+            "secret-based method with no client_secret issued) are instead reported as an "
+            "OAuthRegistrationError before the record is persisted or authorization begins."
+        ),
+        transports=("streamable-http",),
+        note="OAuth is HTTP-only.",
+    ),
     "client-auth:dcr": Requirement(
         source=f"{SPEC_BASE_URL}/basic/authorization#dynamic-client-registration",
         behavior=(

tests/interaction/auth/test_as_handlers.py

@@ -239,10 +239,42 @@ async def test_registration_with_invalid_metadata_is_rejected_with_400(
 
     bad_scope = await http.post("/register", json=body | {"scope": "forbidden"})
     assert bad_scope.status_code == 400
-    body = bad_scope.json()
-    assert body["error"] == "invalid_client_metadata"
+    bad_scope_body = bad_scope.json()
+    assert bad_scope_body["error"] == "invalid_client_metadata"
     # The description embeds a set difference whose ordering is not stable, so assert the prefix.
-    assert body["error_description"].startswith("Requested scopes are not valid: ")
+    assert bad_scope_body["error_description"].startswith("Requested scopes are not valid: ")
+
+    # The server holds no client key to verify a private_key_jwt assertion, so it refuses to
+    # confirm a registration whose every token request it would then reject (RFC 7591 §3.2.2).
+    unsignable = await http.post("/register", json=body | {"token_endpoint_auth_method": "private_key_jwt"})
+    assert unsignable.status_code == 400
+    assert unsignable.json() == snapshot(
+        {
+            "error": "invalid_client_metadata",
+            "error_description": "token_endpoint_auth_method 'private_key_jwt' is not supported",
+        }
+    )
+
+
+@requirement("hosting:auth:as:register-echo")
+@pytest.mark.parametrize("application_type", ["web", "native"])
+async def test_registration_response_echoes_the_registered_application_type(
+    as_app: tuple[httpx2.AsyncClient, InMemoryAuthorizationServerProvider],
+    application_type: str,
+) -> None:
+    """The 201 body reflects the application_type the client registered (RFC 7591 §3.2.1)."""
+    http, _ = as_app
+    body = oauth_client_metadata().model_dump(mode="json", exclude_none=True)
+
+    response = await http.post("/register", json=body | {"application_type": application_type})
+
+    assert response.status_code == 201
+    echoed = response.json()
+    assert echoed["application_type"] == application_type
+    # A secret was issued and no expiry is configured, so RFC 7591 §3.2.1 requires the
+    # response to carry client_secret_expires_at, with 0 (present, not omitted) for "never".
+    assert echoed["client_secret"]
+    assert echoed["client_secret_expires_at"] == 0
 
 
 @requirement("hosting:auth:as:redirect-uri-binding")

tests/interaction/auth/test_discovery.py

@@ -17,14 +17,16 @@ import mcp_types as types
 import pytest
 from inline_snapshot import snapshot
 from mcp_types import ListToolsResult, Tool
-from pydantic import AnyHttpUrl
+from pydantic import AnyHttpUrl, AnyUrl
 
 from mcp.client.auth import OAuthFlowError, OAuthRegistrationError
 from mcp.server import Server, ServerRequestContext
-from mcp.shared.auth import OAuthMetadata, ProtectedResourceMetadata
+from mcp.shared.auth import OAuthClientInformationFull, OAuthMetadata, ProtectedResourceMetadata
 from tests.interaction._connect import BASE_URL, mounted_app
 from tests.interaction._requirements import requirement
 from tests.interaction.auth._harness import (
+    REDIRECT_URI,
+    InMemoryTokenStorage,
     RecordedRequest,
     auth_settings,
     connect_with_oauth,
@@ -174,6 +176,91 @@ async def test_a_400_from_the_registration_endpoint_surfaces_as_a_registration_e
     assert [r.path for r in recorded if r.path in ("/authorize", "/token")] == []
 
 
+@requirement("client-auth:dcr:substituted-metadata")
+async def test_a_registration_response_with_substituted_metadata_completes_the_flow() -> None:
+    """A 201 whose echoed metadata differs from the request still yields a working client.
+
+    The shim replaces the real `/register` with a body that echoes an `application_type`
+    outside OIDC Registration's set, a null `redirect_uris`, and an extra grant type - a
+    substitution RFC 7591 §3.2.1 permits. The registration proceeds and, after `/register`
+    stopped answering, the client authorizes and exchanges a token as normal.
+    """
+    recorded, on_request = record_requests()
+    provider = InMemoryAuthorizationServerProvider()
+    server = Server("guarded", on_list_tools=list_tools)
+    client_id = "substituted-client"
+    provider.clients[client_id] = OAuthClientInformationFull(
+        client_id=client_id,
+        client_secret="s3cr3t",
+        redirect_uris=[AnyUrl(REDIRECT_URI)],
+        token_endpoint_auth_method="client_secret_post",
+        scope="mcp",
+    )
+    body = json.dumps(
+        {
+            "client_id": client_id,
+            "client_secret": "s3cr3t",
+            "token_endpoint_auth_method": "client_secret_post",
+            "application_type": "confidential",
+            "redirect_uris": None,
+            "grant_types": ["authorization_code", "refresh_token", "client_credentials"],
+        }
+    ).encode()
+    app_shim = shim(serve={"/register": (201, body)})
+    storage = InMemoryTokenStorage()
+
+    with anyio.fail_after(5):
+        async with connect_with_oauth(
+            server, provider=provider, storage=storage, app_shim=app_shim, on_request=on_request
+        ) as (client, _):
+            result = await client.list_tools()
+
+    assert result.tools[0].name == snapshot("probe")
+    assert storage.client_info is not None
+    assert storage.client_info.client_id == client_id
+    assert storage.client_info.application_type == "confidential"
+    assert [r.path for r in recorded].index("/register") < [r.path for r in recorded].index("/token")
+
+
+@requirement("client-auth:dcr:substituted-metadata")
+@pytest.mark.parametrize(
+    "credentials",
+    [
+        pytest.param(
+            {"client_secret": "s3cr3t", "token_endpoint_auth_method": "client_secret_jwt"}, id="unimplemented"
+        ),
+        pytest.param({"client_secret": "s3cr3t", "token_endpoint_auth_method": "private_key_jwt"}, id="unsignable"),
+        pytest.param({"token_endpoint_auth_method": "client_secret_post"}, id="secret-not-issued"),
+    ],
+)
+async def test_a_registration_assigning_unusable_credentials_surfaces_as_a_registration_error(
+    credentials: dict[str, str],
+) -> None:
+    """A 201 assigning credentials this flow cannot apply is a registration error.
+
+    RFC 7591 §3.2.1 leaves it to the client to judge whether a substituted value makes the
+    registration usable. The authorization-code flow authenticates with the minted secret, so
+    an unimplemented method, `private_key_jwt` (an assertion it has no key to sign), and a
+    secret-based method with no secret issued are all unusable; each is reported before
+    the record is stored or any authorize/token request is made.
+    """
+    recorded, on_request = record_requests()
+    provider = InMemoryAuthorizationServerProvider()
+    server = Server("guarded", on_list_tools=list_tools)
+    body = json.dumps({"client_id": "unusable", **credentials}).encode()
+    app_shim = shim(serve={"/register": (201, body)})
+    storage = InMemoryTokenStorage()
+
+    with anyio.fail_after(5):
+        with pytest.RaisesGroup(pytest.RaisesExc(OAuthRegistrationError), flatten_subgroups=True):
+            await connect_with_oauth(
+                server, provider=provider, storage=storage, app_shim=app_shim, on_request=on_request
+            ).__aenter__()
+
+    assert storage.client_info is None
+    assert [r.path for r in recorded if r.path in ("/authorize", "/token")] == []
+
+
 @requirement("client-auth:prm-resource-mismatch")
 async def test_prm_with_a_mismatched_resource_aborts_the_flow_before_authorize() -> None:
     """A PRM document whose `resource` does not cover the server URL aborts the flow.