Update MCP server OAuth registration details

Clarified the limitations of MCP servers regarding OAuth dynamic client registration and provided details on using shared bearer tokens.

Author: kennyj42

src/content/docs/cloudflare-one/access-controls/ai-controls/mcp-portals.mdx

@@ -443,7 +443,7 @@ MCP server portals have the following known limitations:
 
 - **Some MCP servers block proxy-based clients.** Certain MCP servers reject requests from proxy-based clients like MCP server portals, returning a `403` error on the registration endpoint. These servers are not compatible with MCP server portals until those providers add Cloudflare as a supported MCP client.
 
-- **Not all MCP servers support OAuth dynamic client registration.** MCP servers that do not support OAuth dynamic client registration cannot use the portal's OAuth authentication flow. For these servers, select **Custom Headers** as the authentication method and provide static credentials (for example, API keys or personal access tokens) instead.
+- **Not all MCP servers support OAuth dynamic client registration.** MCP servers that do not support OAuth dynamic client registration cannot use the portal's OAuth authentication flow. For these servers, you may upload a shared bearer token via the [api](https://developers.cloudflare.com/api/resources/zero_trust/subresources/access/subresources/ai_controls/subresources/mcp/subresources/servers/methods/create#(resource)%20zero_trust.access.ai_controls.mcp.servers%20%3E%20(method)%20create%20%3E%20(params)%200%20%3E%20(param)%20auth_type%20%3E%20(schema)). Static OAuth or per user bearer tokens are not yet supported.
 
 - **Admin OAuth tokens can expire silently.** The admin credential used to [authenticate an MCP server](#reauthenticate-the-mcp-server) is subject to the upstream provider's token expiration policy. When the token expires, the server status changes to **Error** and the server will not appear in the portal for end users. Admins are not notified when this happens. Periodically check the [server status](#server-status) and [reauthenticate](#reauthenticate-the-mcp-server) servers that show an error.