The next version of MongoDB will include SCRAM-SHA-256 as an authentication type. This is defined in RFC 7677. The sample conversation from the RFC is:

 This is a simple example of a SCRAM-SHA-256 authentication exchange... The username
   'user' and password 'pencil' are being used

   C: n,,n=user,r=rOprNGfwEbeRWgbNEkqO

   S: r=rOprNGfwEbeRWgbNEkqO%hvYDpWUa2RaTCAfuxFIlj)hNlF$k0,
      s=W22ZaJ0SNY7soEsUEjb6gQ==,i=4096

   C: c=biws,r=rOprNGfwEbeRWgbNEkqO%hvYDpWUa2RaTCAfuxFIlj)hNlF$k0,
      p=dHzbZapWIk4jUhN+Ute9ytag9zjfMHgsqmmiz7AndVQ=

   S: v=6rriTRBi23WpRR/wtup+mMhUZUn/dB5nLTJRsjl95G4=

In advance of updates to the Auth spec, which will include additional details of mechanism negotiation and user/password normalization (see DRIVERS-444), all drivers should take steps now to ensure their SCRAM libraries are capable of operating in SHA-256 mode, using the sample conversation for verification. (You'll need for force the client nonce to be "rOprNGfwEbeRWgbNEkqO" for the test conversation to work.)