Add support for new Client Credentials Grant Type

[Andrew Lynch]

Is your feature request related to a problem? Please describe.

Per blog post (https://support.box.com/hc/en-us/articles/360056830074-Authenticate-apps-with-Client-Credentials-Grant-Type) the API now supports a Client Credential grant type that simplifies some app access. The post is from Nov 2020 and the last commit on the repo was Oct 2020.

Describe the solution you'd like

Documentation and method support to allow a token to be generated with simply the client_id, client_secret, and enterprise_id (or user as box_subject_type).

Describe alternatives you've considered

Manually generating an access token via RestSharp and a custom call. This requires extra objects and having to parse in the returned access token to the OAuthSession object. No support for autorenew or generating a new token without calling back to custom RestSharp method.

[Patrick Simon]

Hi @lurch89 ,

Thanks for submitting this enhancement request! This is on our roadmap (SDK-1589) as a feature we have prioritized to be implemented in the quarter or two. When we have a more detailed timeline, we can update this GitHub Issue.

We have some other updates coming for the .Net SDK, in the meantime, to bring it up-to-date with the latest API changes.

Thanks so much,

@PJSimon

[Sujay Garlanka]

@lurch89 In the meantime, you can use the following authentication methods found in our docs here.