Fixed url trailing slashes problem

[rghose]

Mainly because of:
return rtrim($this->providerConfig['issuer'], '/') . '/'; in the function used.

[jricher]

This looks like a dangerous change to me because it's doing a kind of normalization on the issuer URL. This can't be guaranteed to be consistent across different IdPs.

[jumbojett]

@rghose Thanks for submitting the pull request. Your code does fix the issue.

@jricher is correct in stating that our library should not be normalizing the URL. I'll be updating the library shortly to remove the for-mentioned code snippet.