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Frequently asked questions#

Common errors#

Source code of flow ... has errors#

Details here.

Source code of flow ... has not been parsed yet#

This may happen when a flow is launched right after its creation and transpilation has not occurred yet. Try again in the next few seconds.

Unable to find a constructor with arity ... in class ...#

A Java invocation of the form Call package.className#new ... is passing a number of parameters that does not match any of the existing constructors for that class.

Unable to find a method called ... with arity ... in class ...#

A java invocation is attempting to call a method that is not part of the given class or the number of parameters passed for the method is not correct.

No Finish instruction was reached#

This occurs when no Finish statement has been found in the execution of a flow and there are no remaining instructions.

Serialization errors#

Agama engine saves the state of a flow (see continuations here) every time an RRF or RFAC instruction is reached. For this purpose the KRYO library is employed. If kryo is unable to serialize a variable in use by your flow, a serialization error will appear in the screen or in the logs. Normally the problematic (Java) class is logged and this helps reveal the variable that is causing the issue. Note variables that hold "native" Agama values like strings or maps are never troublesome; the problems may originate from values obtained via Call.

To fix a serialization problem, try some of the following:

  • Check if the value held by the variable is needed for RRF/RFAC or some upcoming statement. If that's not the case, simply set it to null before RRF/RFAC occurs
  • Adjust the given class so it is "serialization" friendlier. With kryo, classes are not required to implement the interface
  • Find a replacement for the problematic class
  • As a last resort, set serializerType property of the engine to null. Note this will switch to standard Java serialization. This setting applies globally for all your flows

Classes added on the fly#

A class does not "see" other classes in its own package#

This is a limitation of the scripting engine. Here, classes have to be imported even if they belong to the same package, or the fully qualified name used.

How to append data to a flow's log directly?#

Call method log of class io.jans.agama.engine.script.LogUtils. This method receives a variable number of arguments as DSL's Log does. Thus you can do LogUtils.log("@w Today is Friday %th", 13), as in the logging examples.

What Groovy and Java versions are supported?#

Groovy 4.0 and Java 11. The runtime is Amazon Corretto 11.


How to implement localization?#

Store all messages that your templates may show in the jans-auth resource bundle. This can be done by creating files named or in /opt/jans/jetty/jans-auth/custom/i18n. As an example, use to hold the messages translated to Japanese, or for German localized to Switzerland.

The syntax of these files adhere to that of Java properties files. The suffixes xx and YY are driven by RFC 4647 and RFC 5646.

Agama engine will pick the messages from the bundle that best matches the language settings of the end-user browser. Normally, this is supplied through the HTTP header Accept-Language.

A file with no suffix, i.e. is used as fallback when a message cannot be found in specific language/country combination. To learn how to reference a message in a template, visit this page.

How to modify the built-in error pages?#

Agama features some error pages out-of-the-box. They can be customized by editing the corresponding files referenced in the configuration doc page.

Is Javascript supported?#

Yes, the template engine is not concerned about the kind of contents linked in markup. It does not even care if your markup makes any sense. For FreeMarker, templates just produce a textual output.

A flow page is not rendered as HTML, the browser just shows the source code as text#

This is due to lack of proper Content-Type response header. This occurs if your template has filename extension other than ftlh. If you don't want to rename your template, insert <#ftl output_format="HTML"> at the beginning of the file.

How to produce JSON instead of HTML?#

In your templates use <#ftl output_format="JSON"> in the first line. Take a look at the templates whose name start with json_ in folder /opt/jans/jetty/jans-auth/agama. Particularly check how JSON content can be escaped - unfortunately FreeMarker does not support escaping for JSON out-of-the-box.

Development tools#

Are there any IDE or editor plugins available for coding flows?#

Not yet unfortunately. We plan to offer tools in the future to ease the development process.

How to debug flows?#

We plan to offer a debugger in the future. In the meantime, you can do printf-like debugging using the Log instruction. See Agama logging.

About Agama engine#

Does it support AJAX?#

If you require a flow with no page refreshes, it could be implemented using AJAX calls as long as they align to the POST-REDIRECT-GET pattern, where a form is submitted, and as response a 302/303 HTTP redirection is obtained. Your Javascript code must also render UI elements in accordance with the data obtained by following the redirect (GET). Also, care must be taken in order to process server errors, timeouts, etc. In general, this requires a considerable amount of effort.

If you require AJAX to consume a resource (service) residing in the same domain of your server, there is no restriction - the engine is not involved. Interaction with external domains may require to setup CORS configuration appropriately in the authentication server.

I want/need to understand the internals, where to start?#

The quick start guide is a must, followed by Hello world flow for project maintainers. In the end a complete sweep over all the docs is needed.


Does flow execution timeout?#

Yes. The maximum amount of time an end-user can take to fully complete a flow is driven by the configuration of the authentication server and can be constrained even more in the flow itself. Read about timeouts here.

How to prevent launching a flow directly from the browser?#

Disable the flow. It will still be callable from other flows.

Updates in a flow's code are not reflected in its execution#

Ensure the engine is enabled. Use the REST API (PUT method) to update the flow's code. Wait one minute and then retrieve (GET) this flow's data. The property codeError in the response should have the cause.

Why are the contents of a list or map logged partially?#

This is to avoid traversing big structures fully. You can increase the value of maxItemsLoggedInCollections in the engine configuration.

How to add two numbers or compare numeric values in Agama?#

Agama only provides operators for boolean comparison in conditional statements. The structure of an authentication flow will rarely have to deal with computations/comparisons of numbers, strings, etc. In case this is needed, developers have to resort to Java.

How to concatenate strings in Agama?#

See the previous answer. A two-lines solution could be:

strings = [ s1, s2, ... ]
Call java.lang.String#join "" strings

How to know the index of a given loop iteration?#

See the examples in the Looping section of the DSL full reference.

Can Agama code be called from Java?#

No. These two languages are supposed to play roles that should not be mixed, check here and here.

Last update: 2022-09-27
Created: 2022-06-24