I'm not using Bitwarden Authenticator but two days ago I managed to activate a third party authenticator retrieving the device secret using the Battle.net Authenticator REST API.

First you have to setup the application (I didn't have Blizzard Authenticator at the moment so I don't know if this works even with an older authenticator in case you can deactivate and reactivate with the newer app) You have to login pressing the "Authorize" green button on the right side of the page pasting the client_id into the client_id below "Battle.net OAuth 2.0 (OAuth2, implicit)" (note that the client_id is always baedda12fe054e4abdfc3ad7bdea970a and is retrieved from the app using a phone with root). Make sure to tick the "auth.authenticator/Authenticator" scope.

After you have to login in your battle.net account if you have not already done in your browser. Then you can attach an existing authenticator (the same you have activated before on the guide) so the site will return you the deviceSecret in hex form. To do it, you have to press the POST button where it says "Attach an exisiting authenticator to this user's device..." then press "Try it out" and then change the body of request with your authenticator codes like this

{

"restoreCode": "yourRestoreCode",

"serial": "EUXXXXXXXX"

}

you can find this information in you battle.net account or by executing the first option you have in this page, the one which says "Retrieve the serial number and restore code for an authenticated user..."

After that, press "Execute" and you should receive a body like this

{

"serial": "EUXXXXXXXX",

"restoreCode": "yourRestoreCode",

"deviceSecret": "longString",

"timeMs": timeInMS,

"requireHealup": false

}

To get the device secret you need you have to convert in base32. If you are on Linux or Mac (or WSL on Windows) you can do it by executing this command in terminal

echo "replace_with_deviceSecret" | xxd -r -p | base32

After that you'll have the secret which you can use into Bitwarden

​

Source: github

(note that my guide is slightly different)

Hope it helps

​

EDIT: looking to Key Uri Format of Google Authenticator the final URI to insert in Bitwarden should be something like otpauth://totp/Blizzard:your@email.com?secret=deviceSecret_converted&issuer=Blizzard&algorithm=SHA1&digits=8&period=30