Page Comparison

...

1. The user clicks on the link for the external system they wish to access.  By default this opens a new tab that returns a page with a Javascript AJAX handler to request connection information from the handling controller, but there is a portlet preference to replace the existing page. 
2. The handling controller gathers all of the information stored in the HttpContentRequestImpl parameters configuration (basically a list of form fields and values) and readies them for return to the browser
3. All configured Interceptors perform any substitutions on configuration data, such as inserting usernames and passwords.
4. All configured IAuthenticationFormModifier modules run.  These can add additional parameter fields to the result and may perform additional custom logic (depending upon the implementation).  An example of an IAuthenticationFormModifier is a need to contact an external system to get a token that is submitted with the authentication form to the external system.  The custom logic can invoke the external system, parse out the token, and add it as a form field or modify the submit URL to include the token.
5. If the GatewayEntry is flagged as requiring a secure URL (default true), the URL (proxiedLocation) is checked and altered to /HTTPSUrlRequiredButNotSpecified if it was not secure.
6. The controller returns all of the gathered data to the browser (by default a JSON response with caching disabled).
7. The Javascript Ajax handler builds an appropriate html form and submits it to the external system.  As part of this processing, any custom javascript files that are specified for the entry are also executed.  The external system then handles the call and will render whatever page a successful login would render.

...