Login flow with 2fa enabled via modrinth.gg fails

[isXander]

Please confirm the following.

• I checked the existing issues for duplicate problems
• I have tried resolving the issue using the support portal

What browsers are you seeing the problem on?

Firefox

Describe the bug

When signing in to modrinth from the https://modrinth.gg page, the flow is interrupted when it should have opened the 2FA page, instead, it flashes with the main modrinth.gg page and then puts me back on the login page.

When repeating the reproduction steps from https://modrinth.com , I did not have this issue.

Steps to reproduce

1. Ensure you are signed out of Modrinth, and have 2FA enabled on your account
2. Go to https://modrinth.gg
3. Press 'Sign in'
4. Use any of the oauth login methods (I didn't test username/password)
5. Proceed through the 3rd party oauth and authorise
6. See, you are now back on the login page.

Expected behavior

It should correctly continue with the login flow and show the 2FA page.

Additional context

No response

[Erb3]

Able to reproduce. Caused by the oAuth redirect URI being set to Modrinth's sign-in page's redirect query param. Instead the oAuth redirect URI should be the sign-in page URL + redirect query param set.

-https://api.modrinth.com/v2/auth/init?provider=github&url=https://modrinth.com/servers?plan=small
+https://api.modrinth.com/v2/auth/init?provider=github&url=https://modrinth.com/auth/sign-in%3Fredirect%3Dhttps%3A%2F%2Fmodrinth%2Ecom%2Fservers%3Fplan%3Dsmall