Add an option to return the auth request url

[michielgerritsen]

Hello,

Thanks for making this library. I noticed that the createAuthRequest function calls the header function itself to redirect. Because this is hard to test i added an $autoRedirect flag so we can control this behavior, and to be backward compatible.

[pheelixdotcom]

I would like to have this too.

But two things.

1. the default value for the new parameter should be true, to not brake existing functionality.
2. You auto redirect the user if the parameter is false. But to my understanding it should be the other way around

[tareqtms]

Fixed with #44