Using authenticators & panels to have participants "login" across sessions

I've worked out how to 

  1. Create a panel trigger such that when someone submits a survey, they are automatically added to a panel ("account registration"). Check out the survey "Sam test 1" for this. (for the triggers specifically, see advanced options -> triggers -> panel triggers).
  2. Create a "login" for already-created accounts using an authenticator (see "Sam test 3"). Check out the survey flow to see the authenticator. The embedded data under the authenticator I obtained by creating a new embedded data block and hitting "Add from panel" and selecting the appropriate panel (in this case "Sam test panel"). This is EXTREMELY IMPORTANT. It gives us access to "TriggerResponseID", which is our unique identifier.
  3. Automatically log people in to further authenticators using a unique ID accessible only after logging in.
Survey redirects should be placed in CUSTOM END OF SURVEY MESSAGES. This is critical for the redirect after registering and just (IMO) cleaner in all other cases.

To pass a variable to a new survey using a redirect, simply append "&newEmbeddedDataName=${e://Field/embeddedDataName}" to the end of the url for the survey you're redirecting to. (in our case, we will append &TriggerResponseID=${e://Field/TriggerResponseID}).

To bypass the authenticators, ensure that you have an embedded data field called "TriggerResponseID" OUTSIDE THE AUTHENTICATOR. (note that this is different from the login survey, which should have this variable *inside* the authenticator).
Ensure that your authenticator looks like the image below and uses TriggerResponseID as the authentication variable.

The area circled in red is where the magic happens. For ANY AUTHENTICATION YOU WISH TO BYPASS using the unique identifier, you should put the following in this field:

${e://Field/TriggerResponseID} <script>Qualtrics.SurveyEngine.addOnload(function() { this.clickNextButton();  });</script>

This will fill the field with the unique identifier and automatically advance to the next page -- when I tested it, I couldn't even see it happen.

I hope that was clear(ish).

Also worth noting: In the authenticator options, you can choose to reload a participant's progress (meaning that they can come back to the survey later to finish their work). Qualtrics recommends only having one authenticator in the survey if you're doing this, and disabling the survey-wide save and continue option.