How To Get a Form to Fetch Login Data From a *.txt file?

[lacobus]

I know this is very insecure for logins, but this is out of curiosity.

How Would I make a login form but instead of having
If TextBox1.Text = ("username")
and all that stuff how would I make it would get the login data from a *.txt file uploaded
online (i.e. mysite.com/logins.txt) so I could add new users to the list and not make a new version?