/oauth/tokenendpoint are secured by Bearer authentication. To access secured endpoints, you must include a Bearer authentication token in your request header.
Token expiration period: Tokens returned by the authentication endpoint expire in 300 seconds.
Token storage, reuse, and refresh: Always store the token securely in accordance with your organization's security policies. To facilitate token reuse, encrypt and store the token in a file or database. Reuse the token for all API requests made within the token expiration period. Refresh the token shortly before it expires to avoid making unsuccessful requests.
/oauth/tokenendpoint, see the Get an authentication token tutorial.