Authentication is a TIdAuthentication property that contains an object used to perform HTTP Access Authentication for a proxied connection. 

Authentication will normally contain an instance of a TIdAuthentication descendant like TIdBasicAuthentication or TIdDigestAuthentication that implements a specific authentication scheme. 

Applications can assign the Authentication class to be used for the proxied connection. 

If Authentication has not been assigned, and BasicAuthentication is True, a TIdBasicAuthentication object instance will be automatically created in SetHeaders. 

When assigned, Authentication is freed in the Destroy method.

TIdBasicAuthentication 

TIdDigestAuthentication 

TIdProxyConnectionInfo.BasicAuthentication 

TIdProxyConnectionInfo.SetHeaders