Token binding embeds information from an external authentication mechanism, such as a Kerberos server, inside a token. By using token binding, a client can enforce the use of a specified external authentication mechanism with the token. This additional security mechanism ensures that if a token is stolen, for example, it is not usable without external authentication. You configure the authentication types for a token binding in the keystone.conf file: [token] bind = kerberos Currently only kerberos is supported. To enforce checking of token binding, set the enforce_token_bind option to one of these modes: disabled Disables token bind checking. permissive Enables bind checking. If a token is bound to an unknown authentication mechanism, the server ignores it. The default is this mode. strict Enables bind checking. If a token is bound to an unknown authentication mechanism, the server rejects it. required Enables bind checking. Requires use of at least authentication mechanism for tokens. named Enables bind checking. Requires use of the specified authentication mechanism for tokens: [token] enforce_token_bind = kerberos Do not set enforce_token_bind = named. The named authentication mechanism does not exist.