feat(authz): Add remote_json authorizer

[kaorimatz]

Related issue

#201

Proposed changes

Add a new authorizer called remote_json proposed in #201 to support authorizing a request using an external service that doesn't implement the Keto's API interface.

Checklist

• I have read the contributing guidelines
• I have read the security policy
• I confirm that this pull request does not address a security vulnerability. If this pull request addresses a security
  vulnerability, I confirm that I got green light (please contact [email protected]) from the maintainers to push the changes.
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation within the code base (if appropriate)
• I have documented my changes in the developer guide (if appropriate)

Further comments

[aeneasr]

Perfect!

[mostafahussein]

@kaorimatz, How can I send the HTTP Verb (e.g. DELETE) to the remote_json authorizer? For example if the request was about deleting a book so it will look like this

curl -X DELETE http://oath-keeper/books

The remote_json authorizer currently receives /books only, So how can I validate against if the request is Get or Post or Delete and so on. So I can allow or deny based on the request http verb along with the resource

[aeneasr]

That's currently not possible but is a cool idea!

[mostafahussein]

@aeneasr I am trying to figure out what should be added/modified to that code so we can send the http_method (e.g. GET, POST). Any hints?