Add OAuth2 Support #15

[sserrata]

Overview

• Add OAuth2 support for performing token refresh and revocation
• Add support to HTTPClient for auto-refresh
• Add support for storing credentials in ~/.config/pancloud and as environment variables

Implementation

• Added credentials module that supports construction of Credentials object
• Added property methods for retrieving access_token, client_id, client_secret, and refresh_token.
• Add the following methods: _fetch_credentia, get_credentials, remove_profile, refresh, write_credentials.
• Using TinyDB library to upsert and store credentials in JSON format in ~/.config/pancloud directory.
• Added methods revoke_access_token and revoke_refresh_token.
• Added _resolve_credential method which looks for credential in 1) ENVIRON, 2) Credentials file.
• Added region, redirect_uri and auth_base_url variables/attributes.
• Added method get_authorization_url for generating authorization URL and returning state.
• Integrated Credentials with HTTPClient to support auto_refresh and automatic application of access_token to Authorization: Bearer header.

[kevinsteves]

Let's get this in.