AuthManager is going to be changing how some API modules work. For interactive user login, you're going to want to change to using action=clientlogin. The action=createaccount is also going to change to a more interactive flow. The WIP code for the new API modules is in https://gerrit.wikimedia.org/r/#/c/265201/; it's not too late to change stuff in there, but bring good reasons.

Our target is to have this rolling out to WMF wikis by the end of February.

The general procedure for using both of these will be the same:

1. Fetch the initial field information from the new action=query&meta=authmanagerinfo. Using format=json, the relevant part of the data structure is an object with keys being field names and values being objects that include the data type (string, password, select, multiselect, checkbox, button), localized labels, and such.
2. Convert that field information into UI to display to your users.
3. Take the user input and post it to action=clientlogin or action=createaccount, along with some other information documented in those modules.
   
4. The response will tell you what to do next:
   • PASS: You're done, it succeeded.
   • FAIL: You're done, it failed. There's a localized "message" field to tell you why.
   • UI: More user input is needed. There's a localized "message", and there's field information like you got in step 1. You'll repeat steps 2–4 with the new fields (and with slightly different module parameters in step 3).
     The use cases here include requesting the second factor for 2-factor auth, prompting the user to reset their password, informing them that they were renamed from "Example" to "Example~enwiki", etc.
     
   • REDIRECT: It wants you to send the user to another website, e.g. pop up a browser or a web view. Once the remote site is done, it'll send the user to a URL you specified in step 3, at which time you'll extract the data from that request and repeat steps 3–4. There's also provision for skipping the redirect if your app knows how to do a non-web authentication against the provider, e.g. a GoogleLogin extension could provide data that an Android app needs to use some internal Android API to authenticate with a Google account and get the needed data.
     The use case here is for something like "log in with Google", "log in with Facebook", generic "log in with OpenID", and so on where you have to send the user to some other site.
     
   • RESTART: This means that the user authenticated ok, but we don't know what user account the credentials belong to. You could treat this response as if it were UI so they can log in with a different mechanism, or as FAIL, or you could start up action=createaccount to create a new account.
     The use case here is again something like "log in with Google", Google returned success but we don't have any on-wiki account linked with that Google account.
     

Account creation is going to break on day 1, we're not trying to maintain any backwards compatibility there since it wouldn't be likely to work very well anyway and there aren't many account creation clients out there.

The old login with action=login will probably continue to work for users who don't have 2-factor auth, a migrated CentralAuth account (i.e. trying to log in as Example when you're now Example~enwiki), or anything else that would make a UI or REDIRECT response be returned, but again we're not guaranteeing that it won't suddenly stop at some point. Also, the old login mechanism will start returning a "Aborted" or "Failed" (with a localized message) rather than "WrongToken", "BadPassword", "Throttled", and so on.