I recently gone through a blog that explains usage of Yubikeys in SSH. I wonder whether I could use the same method without Yubikey (using my android phone)?
The reffered blog: https://swjm.blog/the-complete-guide-to-ssh-with-fido2-security-keys-841063a04252
The main objective is whenever I try to SSH into a host system from my system, it should pop up Allow/Deny in my mobile phone, like the Google login works
I tried different alternatives of Yubikeys like IDmelon, but couldn't help since my systems are linux based(Ubuntu).
Using FIDO security keys for storing SSH keys is currently implemented in OpenSSH using middleware that uses USB transport.
To use your Android phone as a USB security key would require your phone to be able to communicate using FIDO's CTAP protocol over USB. Android does not support that natively, and I don't know of any app that does, nor if such an app would be allowed to do that on Android.
Android does support CTAP over a tunnel towards web browsers (called hybrid transport, aka cross-device authentication), but that is not supported by OpenSSH.