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HTTP: The Definitive Guide

Cover of HTTP: The Definitive Guide by David Gourley... Published by O'Reilly Media, Inc.

Appendix F. Digest Authentication

This appendix contains supporting data and source code for implementing HTTP digest authentication facilities.

Digest WWW-Authenticate Directives

WWW-Authenticate directives are described in Table F-1, paraphrased from the descriptions in RFC 2617. As always, refer to the official specifications for the most up-to-date details.

Table F-1. Digest WWW-Authenticate header directives (from RFC 2617)




A string to be displayed to users so they know which username and password to use. This string should contain at least the name of the host performing the authentication and might additionally indicate the collection of users who might have access. An example might be "".


A server-specified data string that should be uniquely generated each time a 401 response is made. It is recommended that this string be base-64 or hexadecimal data. Specifically, because the string is passed in the header lines as a quoted string, the double-quote character is not allowed.

The contents of the nonce are implementation-dependent. The quality of the implementation depends on a good choice. A nonce might, for example, be constructed as the base-64 encoding of:

time-stamp H(time-stamp ":" ETag ":" private-key)

where time-stamp is a server-generated time or other nonrepeating value, ETag is the value of the HTTP ETag header associated with the requested entity, and private-key is data known only to the ...

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