libbrillo: policy: Add GetSecondFactorAuthenticationMode for new device policy

Add a new helper function and the matching unit-tests for the the new
device_second_factor_authentication device policy/proto used to control
how the machine secure element hardware can be used to provide a
second-factor authentication in addition to the TPM functionality.

TEST='FEATURES=test emerge-eve protofiles libbrillo'

Change-Id: I9568067a7530c9c0c84142714eb7a67d13e3e45b
Commit-Ready: Vincent Palatin <>
Tested-by: Vincent Palatin <>
Reviewed-by: Dan Erat <>
6 files changed