This function initializes an authentication session using the supported
methods. These are, in order of preference: Digest-MD5,CRAMMD5,LOGIN,
and PLAIN.
Parameter
string
$uid
The userid to authenticate as.
string
$pwd
The password to authenticate with.
string
$method
The requested authentication method.If none is specified,
the best supported method will be used.
Return value
returns Returns a PEAR_Error with an error message on any
kind of failure, or true on success.
