Experiment Center and Auth0 Actions Integration

When an experiment is active, Experiment Center injects the ExperimentContext object into supported Action triggers.

Supported triggers

Experiment context is available for the following Auth0 Actions:

The event.experiment object

In supported triggers, Experiment Center adds an experiment field to the event object:

interface ExperimentContext {
  experiment_id: string;   // The active experiment ID
  variation_id: string;    // The assigned variation ID
  config: {                // Merged configuration: baseline + overrides
    [paramName: string]: { value: unknown };
  };
  is_control: boolean;     // True when this is the control variation
}

When no experiment is active (or when the feature is not enabled for the tenant), event.experiment is null (not undefined).

config object contains the full merged configuration

The config object contains every parameter defined on the feature flag, merged with the assigned variation’s overrides. You never need to look up baseline values or write fallback logic. If the parameter exists on the feature flag, it exists in config.

Null-safety pattern

Check for an active experiment before reading any properties:

exports.onExecutePostLogin = async (event, api) => {
  const ec = event.experiment;
  if (!ec) return; // No active experiment; nothing to do

  // Safe to access ec.config, ec.variation_id, ec.is_control here
};

Use this pattern in all three supported triggers. The early return keeps your Action clean and ensures it behaves correctly during periods when no experiment is running.

Example: post_login, conditional MFA policy

This example reads a boolean parameter and applies a different MFA policy depending on the variation.

// post_login Action
exports.onExecutePostLogin = async (event, api) => {
  const ec = event.experiment;
  if (!ec) return;

  const enforceMfa = ec.config?.require_mfa?.value;

  if (enforceMfa === true) {
    // Treatment variation: enforce MFA for this user
    api.multifactor.enable("any", { allowRememberBrowser: false });
  }
  // Control variation: no MFA enforcement change (baseline behavior)
};

ec.config.require_mfa.value is true for users in the treatment variation and false (the baseline) for users in the control variation. No fallback logic needed.

Example: post_login, set a custom claim based on variation

This example stamps the experiment assignment into the user’s ID token as a custom claim. Some analytics pipelines read token claims instead of tenant logs.

// post_login Action
exports.onExecutePostLogin = async (event, api) => {
  const ec = event.experiment;
  if (!ec) return;

  // Add experiment assignment to the ID token
  api.idToken.setCustomClaim("https://example.com/experiment", {
    experiment_id: ec.experiment_id,
    variation_id: ec.variation_id,
  });
};

Use a namespaced claim URL per the OIDC custom claim convention. The recipient (your app) can then read the claim from the token without querying tenant logs.

Example: pre_user_registration, variation-based metadata

This example uses a registration-flow experiment to set user_metadata based on which variant the registering user lands in.

// pre_user_registration Action
exports.onExecutePreUserRegistration = async (event, api) => {
  const ec = event.experiment;
  if (!ec) return;

  const onboardingVariant = ec.config?.onboarding_variant?.value;

  if (onboardingVariant) {
    api.user.setUserMetadata("onboarding_variant", onboardingVariant);
    api.user.setUserMetadata("onboarding_experiment_id", ec.experiment_id);
  }
};

The metadata is written during registration, so it follows the user across sessions. You can query it later to understand which signup cohort a user belongs to.

Example: post_user_registration, trigger downstream enrollment

This example fires a webhook after registration based on the variation assigned to the new user.

// post_user_registration Action
exports.onExecutePostUserRegistration = async (event, api) => {
  const ec = event.experiment;
  if (!ec) return;

  const enrollInNewProgram = ec.config?.enroll_welcome_program?.value;

  if (enrollInNewProgram === true) {
    await fetch("https://your-backend.example.com/api/enrollment", {
      method: "POST",
      headers: { "Content-Type": "application/json" },
      body: JSON.stringify({
        user_id: event.user.user_id,
        email: event.user.email,
        experiment_id: ec.experiment_id,
        variation_id: ec.variation_id,
      }),
    });
  }
};

Only users in the treatment variation trigger the enrollment webhook. Control users follow the standard post-registration path.

Use is_control

The parameter is_control is true when the user is in the control group (they received the baseline, no overrides applied). Use it when you need to track which users saw the unmodified experience, or when you want to skip optional processing for control users.

exports.onExecutePostLogin = async (event, api) => {
  const ec = event.experiment;
  if (!ec) return;

  if (!ec.is_control) {
    // Only track treatment users in your analytics system
    // (control users are tracked separately, outside the Action)
    await logTreatmentEvent(ec.experiment_id, ec.variation_id, event.user.user_id);
  }
};

For branching on behavior (not analytics), check config parameter values directly. They are more explicit and readable.

Brand Customization

Code Customization

Third-Party Customization

Experiment Center and Auth0 Actions Integration

Supported triggers

The event.experiment object

config object contains the full merged configuration

Null-safety pattern

Example: post_login, conditional MFA policy

Example: post_login, set a custom claim based on variation

Example: pre_user_registration, variation-based metadata

Example: post_user_registration, trigger downstream enrollment

Use is_control

​Supported triggers

​The event.experiment object

​config object contains the full merged configuration

​Null-safety pattern

​Example: post_login, conditional MFA policy

​Example: post_login, set a custom claim based on variation

​Example: pre_user_registration, variation-based metadata

​Example: post_user_registration, trigger downstream enrollment

​Use is_control

Supported triggers

The event.experiment object

config object contains the full merged configuration

Null-safety pattern

Example: post_login, conditional MFA policy

Example: post_login, set a custom claim based on variation

Example: pre_user_registration, variation-based metadata

Example: post_user_registration, trigger downstream enrollment

Use is_control