Get one endpoint's full document by lineKey and endpointId: id, lineKey, name, url, httpMethod, strict, rateLimit, allowedIPs, idempotencyEnabled, senderSignature ({scheme, credentialId}, plus custom for the custom-hmac scheme, or null: whether the sender's signature is verified, never the secret), mock, mockResponse, attributes, targets (auth redacted), and transformers. Each target carries its id, and its secrets come back redacted: the targets array can be edited and sent back in update_endpoint's patch, where a target that keeps its id keeps its stored secrets unless new ones are given. Errors when either argument is missing or when the line or endpoint doesn't exist in this project.