Merge pull request #17 from dajiaji/topic-oidc-example-rp

Fix bug in rp3 to store client/provider information derived from conf.py
Fix bug in adding Authorization header for client authentication in a certain case.

There is a bug in adding an Authorization header in case of using client_secret_basic.
To fix it, a return value of ClientSecretBasic::construct is changed to the same as the return value of BearerHeader::construct.