Generate an OAuth 2.0 access token using the client credentials grant type.

Grant Type: Only client_credentials is supported. This is a server-to-server
authentication flow where your backend server exchanges credentials for an access token.

Token Format: The access token is a JSON Web Token (JWT) containing claims about
permissions and expiration time.

Token Expiration: Tokens typically expire in 900 seconds (15 minutes). The exact
expiration time can be found in:

• The expires_in field (seconds until expiration)
• The exp claim in the decoded JWT (Unix timestamp)