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Flows navigation, UI pages and assets#

RRF is a powerful construct in Agama. Its syntax follows this pattern:

(assignment-var =)? RRF "path-to-UI-template" map-variable?

Execution involves several steps which can be summarized as: location of template, rendering, and user-data retrieval. The process is explained in the following.

Template location#

Note

For convenience, references to the server directory /opt/jans/jetty/jans-auth/agama will be replaced by <AGAMA-DIR> from here onwards.

A path is built by concatenating the Basepath of the flow this RRF belongs to and the actual template path, i.e. path-to-UI-template as in the introductory parapraph. Then the engine's templates path root is prepended to it. The "root" is the value set in the engine configuration for the property templatesPath. Thus, in a default installation, the value to prepend would be <AGAMA-DIR>/ftl.

If there is no such file, the flow will crash right away, otherwise, processing continues.

How to build templates?#

Templates are expected to be written using Apache FreeMarker. This is a simple and highly productive language to produce HTML and other forms of output. By convention templates generating HTML markup in Agama should have the extension ftlh. Practically they will look and behave as regular HTML files.

Developers are encouraged to take a peep at the FreeMarker manual before trying to write their first pages. It usually boils down to produce the desired markup plus adding some placeholders for information that is dynamic. The key concept there is Template + data-model = output which is pretty natural. The sumation in this equation is generally referred to as "rendering a template" in this documentation.

Rendering#

Rendering is the process of "injecting" the variable passed (map-variable in the above) into a template. If no variable is present in the instruction, it is assumed an empty map was passed, i.e. { }.

The variable injected ("data model" in FreeMarker terms) always has to be an Agama map, Java bean or object implementing the java.util.Map interface. This will allow access to the contents of such variable from within the template.

Here is a simple example. Suppose you want to ask for a username and password in a page called login.ftl and that such page will be stored in <AGAMA-DIR>/ftl/myflow/pages/login.ftl. Assume the flow has the header directive Basepath "myflow". Also, let's say we want to pass a custom salutation message to be shown at the top of the page. Here is how the Agama code would look like:

...
obj = { message: "Hey ho!, let's go" }
RRF "pages/login.ftl" obj
...

And here the UI page contents:

<!doctype html>
<html xmlns="http://www.w3.org/1999/xhtml">
    ...
    <body>

        <h1>${message}</h1>         

        <form method="post" enctype="application/x-www-form-urlencoded">
            <div>
                <label for="username">Username</label>
                <input type="text" name="username">
            </div>
            <div>
                <label for="password">Password</label>
                <input type="password" name="password">
            </div>
            <input type="submit" value="Login">
        </form>

    </body>
</html>

Extended data model#

The data model (injected map) is attached some additional keys for convenience:

  • webCtx. It gives easy access to often needed bits like current path, locale, etc. This is a Java object you can inspect here. Take a look at the getters; writing ${webCtx.contextPath} in a template will insert the result of calling method getContextPath - normally the string /jans-auth.

  • msgs. It gives access to the localized messages of jans-auth application. Some developers might know this as the "internationalization labels" or "resource bundle" of an application. This is a collection of .properties files where common UI-related messages in different languages can be found. A message (label) is identified by a key, so in a template ${msgs.<KEY>} could be used. As most keys in resource bundles have dot characters, the alternative notation ${webCtx["KEY"]} works better for FreeMarker, for example ${msgs["login.errorMessage"]}.

  • cache. Allows developers to retrieve values already stored in the Jans configured cache, e.g. ${cache.myKey}. To avoid template errors in case of a cache miss, you can use Freemarker's safeguard expressions. Note you cannot store/modify values in the cache from templates.

Assets handling#

Clearly, templates can link other local web resources like Javascript code, images, etc. The location of this kind of files is expected to be in the filesystem under <AGAMA-DIR>/fl directory. Note this is not the same directory of templates. Doing so would allow users to retrieve the code of templates by simple URL manipulation.

As an example, suppose your flow Basepath is foo and you have the instructions RRF index.ftlh and RRF bar/index2.ftlh somewhere in your code. Then your local <AGAMA-DIR>/ftl would look like:

foo
|- index.ftlh
+- bar
   \- index2.ftlh

Say index.ftlh has markup like <img src="bar/me.png"> and index2.ftlh has <link href="my/style.css" rel="stylesheet"> somewhere. This is how <AGAMA-DIR>/fl would look like:

foo
+- bar
   |- me.png
   \- my
      \- style.css

User-data retrieval#

Once the rendered page is shown in the browser, the flow execution is literally paused. If the user stands idly at this page, nothing will happen. To make the flow proceed, an HTTP POST must be made to the current URL. This is exactly what login.ftl of the above example tries to do: it provides a button that submits the form via POST for the flow to resume execution.

Once the flow continues, an Agama map is built using all form fields received at the server and bound to the variable used in the assignment of the RRF instruction (the variable referred as assignment-var in the introduction of this page). This only applies when RRF has an assignment associated, of course.

If the earlier example is modified to

...
obj = { message: "Hey ho!, let's go" }
credentials = RRF "pages/login.ftl" obj
...

the form values can then be referenced as credentials.username and credentials.password in the flow. In other words, the keys of the resulting map will correspond to the form field names. The values will all be strings.

3-param variant#

In the Jans Agama engine, RRF can be passed a third parameter: RRF templatePath variable boolean. When the boolean value is true the callback URL will be available while RRF is in execution (as in RFAC). In this case, if the callback is visited, data passed to it will be set as the result of the RRF. If a POST to the current URL is received first, i.e. callback not hit, behavior will be as in the two-param RRF invocation. This is also the case when a false value is passed for the third parameter.

The three-param variant of RRF can be useful when:

  • The decision to redirect to an external site can only be done from the browser itself
  • The external site expects to receive an HTTP POST. In this case, the rendered template may contain a form with fields as needed plus auto-submission logic in Javascript to perform the actual POST. This typically occurs in inbound-identity flows where identity providers require authentication requests serialized in application/x-www-form-urlencoded format as is the case of SAML HTTP POST binding, for example
Last update: 2024-08-19
Created: 2023-06-06