How Can a Protocol Document Authentication Requirements?
From the earlier reference collection. Read the current software blog.
Authentication documentation should identify credentials, their transport protection, the permissions they carry, and clear failure behavior.
Name the credential and its handling
A protocol should tell implementers what credential a client presents and where it goes. It might be a token in a request header, a certificate established during a connection, or another explicitly defined mechanism. State the syntax, whether the credential is required for every request, and how it is obtained or renewed if that is within the protocol’s scope.
Avoid examples that encourage placing secrets in URLs, logs, or ordinary diagnostic output. URLs are frequently copied into histories and intermediary logs. If a protocol uses a header or another protected channel, show the credential as a placeholder and explain that deployments must supply the real value through an appropriate secret-handling mechanism.
Separate identity from permission
Authentication identifies or verifies a client; authorization determines what that client may do. Documentation should list the permissions or scopes needed for each operation. For example, reading a public status might require no credential, while changing a user’s settings could require a token with a narrowly defined write scope. This lets clients request only the access they need and helps operators diagnose an authorization failure.
Be precise about whether credentials are tied to a person, an application, a device, or a particular session. Also describe expiration and revocation behavior when defined by the system. If credentials can be renewed, identify which party initiates renewal and how a client learns that renewal is needed.
State channel protections
Explain what transport protections are required when credentials or private data are sent. A protocol should not imply that a credential is safe merely because it is encoded or obscured. Require a protected transport where appropriate, and identify any additional protections such as certificate validation that clients must apply. Keep these requirements distinct from message-level authentication so implementers can understand which layer provides each property.
Give a complete but sanitized example showing where the credential belongs, how the request is formed, and which response indicates success. Make clear that sample values are illustrative and must not be copied as real credentials.
Define failures and recovery
Document the expected responses for missing, invalid, expired, and insufficiently scoped credentials. A missing or invalid credential may call for reauthentication; insufficient scope may require an administrator to grant a permission. Clients should not retry unchanged credentials indefinitely. If the protocol has stable error codes, connect them to these cases and state which details are safe to show to a user.
A useful authentication section lets a developer answer four questions without guessing: what to send, how to protect it, what access it grants, and what to do when the server refuses it. That clarity helps prevent both insecure handling and unhelpful client behavior.