TIdDigestAuthentication = class(TIdAuthentication);

TIdAuthenticationDigest is a TIDAuthentication descendant that implements the HTTP Digest Access Authentication Scheme, as described in the Internet Standards documents: 

RFC 2617 - HTTP Authentication: Basic and Digest Access Authentication  

TIdAuthenticationDigest extends the ancestor class by providing internal properties and methods needed to create the message digest returned in the authentication string. This is includes values in the format: 

Digest username="jdoe" realm="http://www.domain.com" result="00112233445566778899aabbccddeeff"

TIdAuthenticationDigest provides an overridden DoNext method that reads the values for the message digest and stores the arguments in the following internal properties: 

An EIdInvalidAlgorithm will be raised if the Algorithm read for the message digest contains a value other than 'MD5'.