Connection should support authParamsMap

[nicosabena]

In addition to #12, it would be good to directly support the authParamsMap options in the connection definition.

The authParamsMap provides a way to map parameters received in the authentication call into the authorization call sent to the external identity provider. For example:

{
  "options" : { 
    "authParamsMap" : {
      "foo": "bar"
    }
}      

Now if I do tenant.auth0.com/authorize?....&bar=something, the value will be mapped into a call like idp.com/authorize?....&foo=something.

[nicosabena]

Update: Auth0 whitelists the /authorize call, so values on the right side (i.e. from the auth0domain/authorize call) can only be:

'force_login', 'login_hint', 'whr', 'wauth', 'hd', 'access_type', 'prompt', 'approval_prompt', 'display', 'include_granted_scopes', 'resource'

(code here)