credential

n. [ Cf. It. credenziale. ] 1. That which gives a title to credit or confidence. [ 1913 Webster ]

2. pl. Testimonials showing that a person is entitled to credit, or has right to exercise official power, as the letters given by a government to an ambassador or envoy, or a certificate that one is a duly elected delegate. [ 1913 Webster ]

The committee of estates excepted against the credentials of the English commissioners. Whitelocke. [ 1913 Webster ]

Had they not shown undoubted credentials from the Divine Person who sent them on such a message. Addison.