How can one add a mfa solution like saas pass to this? Or do you add it?
It's the job of the application to prompt caller for 2FA input and verify it using the provider/device of your choice.
But to save you time even with that implementation, ASPSecurityKit has a category of products called source packages, which provide full implementation of several commonly needed functionality, including 2FA workflow [1], installed right into your project as source code, so you can switch to any MFA provider easily by modifying the code that sends MFA token to the device.
0: https://aspsecuritykit.net/docs/article/the-security-pipelin...
1: https://aspsecuritykit.net/docs/article/source-packages/?pac...