Forms authentication has an option to use a web.config based authentication. One of the possible encryption algorithms is sha1. To calculate it, you can create a tool in c# (I even did that, but.. I lost it when my drive crashed) or you can use python.
It’s as simple as
1: import sha
2: sha.sha('<password goes here>').hexdigest()
There are probably many other ways to do that, but you must admit, this is a quick one