Device Code Authorization Grant

[codefiesta]

Description

Implements the device code authorization grant workflow to allow tvOS (or any other apps that don't have access to a web browser) to leverage OAuthKit.

The Device Code Authorization Grant Workflow consists of the following:

1. Request Device Code:

• The OAuth client initiates the authorization process by sending a request to the provider deviceCodeURL with the clientID and desired scopes.
• This request returns a device code, a user code, a verification URI, and an interval indicating how often the app should poll for authorization.
• The user code is displayed to the user, and the verification URI is the URL they should visit in a web browser.

2. User Authorization:

• The user opens the verification URI in a web browser and enters the provided user code.
• The user authenticates with the provider, granting the app the requested permissions.

3. App Polling for Authorization:

• While the user is entering the code, the OAuth client will be polling the accessTokenURL endpoint in the background.
  This polling continues until the user completes the authorization, or the device and user codes expire.
• The client_id and device_code obtained in step 1 are used in these polling requests.
• The grant_type must be urn:ietf:params:oauth:grant-type:device_code.

See:

• https://auth0.com/docs/get-started/authentication-and-authorization-flow/device-authorization-flow
• https://www.oauth.com/playground/device-code.html

Fixes #4

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

[codefiesta]

⚠️ NOTE: Sending the GrantType is the breaking change in this PR. Downstream apps will need to update or stay at the 0.0.5 tag until they can update.