Split up authenticate() into individual actions to allow per-action use

[bartgloudemans]

Allowing the caller to call the magical request handler authenticate or to have more control over the process and call the individual actions themself

• [x] Added public methods per action (requestAuthorization, handleCode, handleClaims)
• [x] authenticate() makes use of newly created atomic actions

[ricklambrechts]

Thanks for this PR! Overall I think this is a nice improvement that enables more extensibility.

This change also adds the ability to use specific $_GET or $_POST params instead of the $_REQUEST param by just overriding the updated authenticate function.

I noticed that the updated code has tabs instead of spaces, mabye you can update the code to use spaces.

[bartgloudemans]

@ricklambrechts Thanks for the feedback and sorry about the tabs, will correct those