code: public String getAuthorizationUri(List<Scope> scopes, String redirectUri, String state) {
  		return getAuthorizationUri(scopes, redirectUri, state, null, null);
  	}
docs: Generate URI used during oAuth authorization
  Redirect your user to this URI where they can grant your application
  permission to make API calls
  @see <a href="https://www.wepay.com/developer/reference/oauth2">https://www.wepay.com/developer/reference/oauth2</a>
  @param scopes             List of scope fields for which your application wants access
  @param redirectUri      Where user goes after logging in at WePay (domain must match application settings)
  @param state    The opaque value the client application uses to maintain state.
  @return string URI to which you must redirect your user to grant access to your application