ProxyParams is a published TIdProxyConnectionInfo property in TIdHTTP, and represents values used in an HTTP request that requires a Proxy connection. 

ProxyParams contains properties that relect the Server, Port, Username, and Password used to open and authorize a connection to a Proxy server. ProxyParams also indicates if authentication uses the Basic Authentication algorithm. 

ProxyParams is used when TIdHTTP attempts to set the Host and Port number for the client connection, and when OnProxyAuthorization is triggered for the client connection. The Header representation for ProxyParams is used when the HTTP Protocol handler builds the HTTP request packet and tranmits its content to the host server. 

The Authetication mechanism in ProxyParams is reset when the OnDisconnected event handler is triggered for the HTTP client connection.

TIdProxyConnectionInfo 

TIdHTTPProtocol 

TIdAuthentication 

TIdHTTP.OnProxyAuthorization