Connect an agent

The full suite, not a thin wrapper. Emission, reception and the tax layer are all here.

Direct execution, with an escape hatch for whoever wants one. The MCP client's own tool-approval step is the default human in the loop. Empresas that want more can turn on a two-step draft-and-confirm.

Being AI-first means resolving ambiguity, not refusing it. draft_document takes a receptor (the recipient) by name, because that is how a person talks to an agent. Line items are structured ([{description, quantity, unit_price}]): the model does the prose, because it understands prose better and more cheaply than any parser we could write, and draft_document returns the totals so the person sees them before anything is signed. There is no prose parser in the API and there will not be one: a parser hidden behind an endpoint turns a misread quantity into a tax document.

How the client identifies itself. The MCP spec sets a priority order for how a client says who it is: a pre-registered client first, then a client ID metadata document (CIMD), and dynamic registration last, as the fallback.

• Client ID metadata document (CIMD). The client can use an https URL as its client_id — for example https://claude.ai/.well-known/oauth-client.json — instead of registering before it connects. The server fetches it at connect time (GET, 3 s timeout, 32 KB max, no redirects, never to a private or loopback address) and validates the JSON: the client_id the document declares has to be exactly that URL, client_name and redirect_uris are required, and only public clients are accepted (token_endpoint_auth_method absent or "none", PKCE S256 as always). The result is cached honoring Cache-Control: max-age, clamped between 1 and 24 hours — an error is never cached. The redirect_uri of every authorization has to match one the document declares exactly, the same rule as a registered client — with one exception, RFC 8252 §7.3's: when the document declares http://localhost/… or http://127.0.0.1/…, the port is not compared, because a native client such as Claude Code opens a different one every session.
• Dynamic client registration (RFC 7591). The fallback for a client that does not yet publish a CIMD — Cursor, VS Code, Windsurf, ChatGPT and similar still register this way. Any MCP client registers itself on first connection — no prior approval, no application allowlist. Registration returns a public client_id; there is no client_secret, because PKCE is the confidentiality mechanism for a public client that cannot keep a secret.

POST https://mcp.facturia.cl/register        (RFC 7591)
GET  https://mcp.facturia.cl/.well-known/oauth-authorization-server

That same GET declares whether the server accepts CIMD:

{ "client_id_metadata_document_supported": true }

What the person sees on the consent screen. With a CIMD client the screen shows its name and the origin of its metadata document ("Claude · claude.ai") — that origin is verifiable, because that is where the document lives. A dynamically registered client still gets the warning "This application registered itself and picked its own name — we do not verify it." In both cases the screen keeps showing the host the authorization code will be sent to ("Where this is going"), with an extra warning when that host is localhost or 127.0.0.1.

Authorization and consent. Standard authorization-code + PKCE flow. The consent screen is not a rubber stamp: that is where you decide which Facturia credential the grant wraps.

GET https://mcp.facturia.cl/authorize
  ?client_id=mcpc_01K2SC9X4M
  &redirect_uri=https://claude.ai/api/mcp/auth_callback
  &response_type=code
  &code_challenge=E9Melhoa2OwvFrEMTJguCHaoeK1t8URWbuGJSstw-cM
  &code_challenge_method=S256
  &scope=documents:read documents:write tax:read
  &state=af0ifjsldkj

Token. POST /token exchanges the code (with the PKCE verifier) for a short-lived access token and a longer-lived refresh token, revocable on its own.

{
  "access_token": "mcpat_9lQpV3fA2mKcRt7wZxYb1Nde",
  "token_type": "bearer",
  "expires_in": 3600,
  "refresh_token": "mcprt_qT8vN2wLmR5xKpJ7hYdCbA3s",
  "scope": "documents:read documents:write tax:read"
}