You would probably have to have two separate proxy crates to handle old/new logins and a way to either detect which to use, or try the other on failure of the first.
So your dep tree would look something like:
[your crate]
|
|-> [argonrs_old]
| |
| |-> [argonrs v1]
|
|-> [argonrs_new]
|
|-> [argonrs v2]