Khoj Open Redirect Vulnerability in Login Page

Summary

### Summary An attacker can use the `next` parameter on the login page to redirect a victim to a malicious page, while masking this using a legit-looking `app.khoj.dev` url. For example, `https://app.khoj.dev/login?next=//example.com` will redirect to the https://example.com page. ### Details The problem seems to be in this method: https://github.com/khoj-ai/khoj/blob/2667ef45449eb408ce1d7c393be04845be31e15f/src/khoj/routers/auth.py#L95 ### PoC Open the `https://app.khoj.dev/login?next=//example.com` url in a Gecko-based browser (Firefox). ### Impact The impact is low, and this could only be used in phishing attempts, but it's still a problem nonetheless.