oauth2c is a command-line tool that simplifies the process of
experimenting with different grant types and client authentication
methods for OAuth 2.0.

* Simple and intuitive interface for quickly experimenting with
  different OAuth 2.0 grant types and client authentication methods
* Supports all modern OAuth 2.0 grant types: authorization code,
  implicit, password, client credentials, refresh token, JWT bearer
* Supports all client authentication methods: client secret basic,
  client secret post, client secret JWT, private key JWT, TLS client
  auth

Homepage:
https://github.com/cloudentity/oauth2c/
