sub login_user {
    my ($self,$authenKey,$courseName,$userID) = @_;
    my $soapEnv = new WebworkSOAP($authenKey,$courseName);
    my $newKey;
    my $timestamp = time;
    my @chars = @{ $soapEnv->{ce}->{sessionKeyChars} };
    my $length = $soapEnv->{ce}->{sessionKeyLength};
    srand;
    $newKey = join ("", @chars[map rand(@chars), 1 .. $length]);
    my $Key = $soapEnv->{db}->newKey(user_id=>$userID, key=>$newKey, timestamp=>$timestamp);
    eval { $soapEnv->{db}->deleteKey($userID) };
    eval { $soapEnv->{db}->addKey($Key) };
    $@ and soap_fault(SOAPERROR_USER_NOT_FOUND,"User not found.");
    my $log_msg = "LOGIN OK: user_id=$userID login_type=SOAP";
    writeCourseLog($soapEnv->{ce},"login_log",$log_msg);
    return SOAP::Data->type( 'string', $newKey );
}