Add OAuth2 Client ID Metadata Document support

MCP connectors such as ChatGPT and Claude register via HTTPS
client_id URLs instead of pre-provisioned GIDs. Fetch and cache
their metadata documents, upsert clients on first use, and
advertise CIMD in OIDC discovery when allowed URLs are configured.

Signed-off-by: Bryan Frimin <bryan@probo.com>

pkg/coredata/migrations/20260619T094531Z.sql

@@ -0,0 +1,22 @@
+-- Copyright (c) 2026 Probo Inc <hello@probo.com>.
+--
+-- Permission to use, copy, modify, and/or distribute this software for any
+-- purpose with or without fee is hereby granted, provided that the above
+-- copyright notice and this permission notice appear in all copies.
+--
+-- THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
+-- REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
+-- AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
+-- INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
+-- LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
+-- OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
+-- PERFORMANCE OF THIS SOFTWARE.
+
+-- Store the HTTPS client_id URL for OAuth Client ID Metadata Document (CIMD)
+-- clients registered on first use (e.g. ChatGPT, Claude MCP connectors).
+ALTER TABLE iam_oauth2_clients
+ADD COLUMN external_client_id TEXT;
+
+CREATE UNIQUE INDEX iam_oauth2_clients_external_client_id_unique
+ON iam_oauth2_clients (external_client_id)
+WHERE external_client_id IS NOT NULL;