MCP OAuth and protocol reference for client developers

SignWith follows the MCP authorization specification. Clients that support it can connect with just the server URL, https://app.signwith.co/mcp.

Discovery

An unauthenticated request returns 401 with a WWW-Authenticate header that points to the protected resource metadata:

HTTP

WWW-Authenticate: Bearer resource_metadata="https://app.signwith.co/.well-known/oauth-protected-resource/mcp", scope="read write"

The authorization server metadata is at https://app.signwith.co/.well-known/oauth-authorization-server.

Authorization


Flow	Authorization code with PKCE (`S256` only)
Client registration	Dynamic Client Registration at `/oauth/register`, or Client ID Metadata Documents
Resource indicators	Tokens are bound to `https://app.signwith.co/mcp`
Scopes	`read` and `write`
Access tokens	1 hour
Refresh tokens	60 days, rotated on use
Revocation	`/oauth/revoke`
Responses	Include the `iss` parameter

On the consent screen, people choose Full access (read and write) or View only (read). They can see and disconnect connected apps in Settings → Connected apps.

OAuth tokens only work on /mcp. To call the REST API, use an API key.

Errors and limits

If an authorization request from a client that registered itself (Dynamic Client Registration or a Client ID Metadata Document) is invalid, SignWith usually shows the error on its own page instead of redirecting back to the client. Claude and ChatGPT still get the standard OAuth error redirect. Check the request against the authorization server metadata.
The unauthenticated OAuth endpoints are rate limited per IP address: /oauth/authorize and /oauth/token at 60 requests a minute each, and /oauth/register at 30 an hour. Over the limit, /oauth/token returns 429 with the error slow_down.

API keys instead of OAuth

A client can skip OAuth and send an API key in the Authorization header:

HTTP

Authorization: Bearer sw_live_...

A read-only key behaves like a View only connection.

Protocol behaviour

Transport is Streamable HTTP, and the server is stateless. It only answers POST requests; GET and DELETE return 405.
Supported protocol versions: 2025-06-18, 2025-03-26 and 2024-11-05.
Methods: initialize, ping, tools/list and tools/call.
JSON-RPC messages without an id are notifications: they aren't executed and get no response. A request made only of notifications returns HTTP 202. An empty batch returns error -32600.
A failed tool call returns a normal result with isError: true, and the API's error code and message in the content.
Each tool call runs the matching REST API request, so rate limits (300 requests a minute per connection), credits and validation are the same.

The tools and their arguments are on the MCP tools page.