Set the password.
This function sets the password in the userinfo to the string. Reserved characters in the string are percent-escaped in the result.
The interpretation of the userinfo as individual user and password components is scheme-dependent. Transmitting passwords in URLs is deprecated.
assert( url("http://user@example.com").set_password( "pass" ).encoded_userinfo() == "user:pass" );
this->has_password() == true && this->password() == s
Strong guarantee. Calls to allocate may throw.
userinfo = [ [ user ] [ ':' password ] ]
user = *( unreserved / pct-encoded / sub-delims )
password = *( unreserved / pct-encoded / sub-delims / ":" )