PSN Environment fixed for class setup

Merge pull request #5 from OffBase/v0.1.7

V0.1.7

Fixed Callback Phase

Redirect uri was not matching previous redirect uri, which is checked by PSN. Since code and state params are added after the authorization call, callback_url was causing this error.
Added Authorization headers properly.

Use of configuration variable

Merge pull request #3 from OffBase/0.1.4

Updated version after adding configuration variable

Use of rails secrets

0.1.4

Changed variable from constant, for rails secrets

Initial strategy implementation

0.1.3

Updated version after update