Hi Drew, if you already have a list of logins, then as you're suspecting, you can make a contact list and assign a unique logins to each contact as embedded data. Within the survey itself, you just need to ensure that you know who is submitting the response so that you can provide them with the corresponding login. If you're distributing the survey via individual links, then you can simply pull the login into your survey response as an embedded data field (pulled from the contact panel) and present it to your respondent via piped text. If using an anonymous link, then you can add an authenticator to the survey flow to identify the respondent when they agree to participate. With the respondent identified, you can pull the relevant login into an embedded data field and present it via piped text.
Hope that helps!
Cheers,
Cameron

Thanks Cameron but I don't know them in advance. A random person will become participant 1, then 2 and so on. I don't know of a way to use piped text to pick the next available contact to display, never duplicating.

Hi Drew, thanks for the additional info. Am I correct in understanding that you have a pre-defined list of logins, but you do not have prior knowledge of any prospective respondents? Also, is there a consistent format for the pre-defined logins?
If the format is something like "Participant1", "Participant 2", etc, then I think you could leverage quotas to achieve the desired outcome in combination with an embedded data field.
Essentially, you can increment a quota when someone agrees to participate. So if the quota begins at 0, then the first respondent who agrees to participate will increment the quota (i.e. quota is now equal to 1). Per the screenshot below, you could then use branch logic such that when a respondent agreed to participate, you can set an embedded data value (e.g. "Login") to be "Participant+Quota" (with Quota being piped text). That would allow you to systematically assign unique and consecutive logins to each new participant. The unique login would also be saved into the survey response via that embedded data field, meaning you can easily report out on the login allocated to each participant.
Cheers,
Cameron

That sounds pretty good CamM for handing out login usernames. I clever way of using a quota to iterate through them.
Now the passwords are unique and not predictable. Knowing the username, based on what you were suggesting before, is there a way to find a user in a contact list and then display a related field on that contact? When you said "With the respondent identified, you can pull the relevant login into an embedded data field and present it via piped text." I've never used the branch on authentication option.

Hi Drew, coincidentally, I was answering a very similar question the other day. Check out this solution as I think it will give you the info you are needing.
Cheers,
Cameron