Add login with API Access Token

[bvoilar]

Description

Add support for authentication using API Access Tokens. The authentication follows RFC6749 (OAuth 2.0). If the user argument of the login cli is set to "api_token" the session-id is interpreted as API Access Token. An oAuth 2.0 authentication request is made to the token endpoint and the access_token from the response is used as session-id. Furthermore, the pyvcloud client's rehydrate_from_token function must be called with the optional argument is_jwt_token=True.

API Access Token authentication is useful when vCloud Director is configured to authenticate through an external identity provider.

Implements feature request: #581

Usage

1. Generate an API Access Token
2. Login with the generated API Access Token

   vcd login <VCD_HOST> <VCD_ORG> api_token --session-id <API_ACCESS_TOKEN>
   

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