Authentication with Password from Database

Hello,

we have a project where multiple users are only represented by one user in WordPress itself.

I am trying to login the users into WordPress when the external authentication was successful. When i get the correct username and password from the WordPress database the password is md5-hashed, but I need the plain-text password to authenticate the user in WordPress.

Is there any way to authenticate users in the code with php, without having the plain-text-password of a user (but only the md5-version)?