Modify URL generation with a fragment

Signed-off-by: Grigoriev, Nikolai nikolai.grigoriev@nuance.com

#345, ory/hydra#1201

Proposed changes

Go's URL class does not seem (to me) to be well designed for constructing the URLs. It seems to be impossible to avoid double-encoding of the characters if one used url.Fragment populated using url.Values.Encode().

The proposed change encodes the fragment separately using url.Values.Encode(), ensures that the original redirect URL does not have a fragment (it must not have one by RFC). Then it constructs the URL string and, if the fragment is not empty, adds the raw encoded fragment to the URL.

Checklist

• I have read the contributing guidelines
• I confirm that this pull request does not address a security vulnerability. If this pull request addresses a security
  vulnerability, I confirm that I got green light (please contact hi@ory.sh) from the maintainers to push the changes.
• I signed the Developer's Certificate of Origin
  by signing my commit(s). You can amend your signature to the most recent commit by using git commit --amend -s. If you
  amend the commit, you might need to force push using git push --force HEAD:<branch>. Please be very careful when using
  force push.
• I have added tests that prove my fix is effective or that my feature works
• [n/a] I have added necessary documentation within the code base (if appropriate)

Further comments

This is my first Go experience so I will appreciate any comments and suggestions