Incorrect password after upgrade to .net core

I am using asp.net 4.6.1 using native UserManager to handle Register / Login flow. After upgrading to .net core 1.1, it turned out that the hash algorithm had changed, so users were unable to log in using the old password.
For example, the password "P @ ssword123" was hashed as the "ABiX7922FWETSxMXAlvD91GI1HwQSmb4ArreR + wa3R9bbz13 / ITuwxshQjnIg30Zsw ==" , but the new value is hashed to generate the .net core is "AQAAAAEAACcQAAAAECMDFIuBWc4dTtEuLL6RUfszQLjnWzluDNUFNuCPWBqlLzgVx0ASLWvBUTuShLnulQ =="

Does anyone have an idea to change the .net core hash algorithm so that it can be backward compatible with the old asp.net 4.6 framework?