Custom connector only offers OAuth fields for an API-key-authenticated MCP server (Deckbase) — no "Request headers" option available

### MCP server URL or name

https://www.deckbase.co/api/mcp

### How are you connecting to this server?

From a custom connector URL I entered manually

### Where does the issue occur?

When pressing the Connect button

### When did you last reproduce this?

2026-08-02, 17:30 CEST

### Browser and OS

Claude Desktop app on Windows 11 Pro (not browser-based)

### Describe the issue

I'm trying to connect Deckbase (a flashcards app) as a custom connector via its remote MCP server. Deckbase authenticates via a static API key sent as an "Authorization: Bearer " header, not OAuth. When adding it through Customize > Connectors > Add custom connector, the "Advanced settings" section only shows fields for "OAuth Client ID" and "OAuth Client Secret" — there is no "Request headers" field available on my account. When I click Connect, Claude attempts an OAuth flow anyway, which fails because Deckbase's server has no OAuth client registered.

### Error details

```shell
Claude.ai showed a generic connection failure after clicking Connect.
The browser tab opened by the OAuth redirect showed:
{
"error": "invalid_client",
"error_description": "Unknown client_id"
}
```

### Expected behavior

Since Deckbase (and presumably other MCP servers using simple API-key auth) doesn't implement OAuth, I'd expect to be able to authenticate via a static header (e.g. Authorization: Bearer ) when adding a custom connector — either because this is generally available, or because my account gets access to the header-authentication beta mentioned in Claude's documentation.

### Additional context

I've confirmed with Deckbase support that their MCP server only supports API-key/Bearer token auth, with OAuth not currently planned. My account's "Add custom connector" dialog shows only OAuth Client ID/Secret fields, suggesting the header-based auth beta hasn't rolled out to my account yet.

No repository files or tests are named in the report. Start by reproducing the custom connector flow in Claude Desktop on Windows and inspect the Advanced settings and OAuth redirect behavior; done means a custom connector can supply an Authorization bearer header and connect to Deckbase without requiring OAuth.

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