[Email_DigestResponse] is a helper method which is used internally by the POP and SMTP tags in order to process DIGEST-MD5 authentication.

The method expects a single parameter which is a map containing the elements of the response to a digest challenge from a remote server. The map may contain elements for charset, username, nonce, nc, cnonce, digest-uri, password, realm, and response.

The method returns a string with the formatted response to the digest challenge.