ITokenAcquisition.GetTokenForUser() needs to take an optional userFlow parameter

[jmprieur]

Why?
Today we don't specify in the controllers which policy/user flow to use to acquire the token, and therefore the B2C scenarios is not quite right.

What?
Expose a userFlow parameter and lookup the right account in the implementation

See also the 2 related issues

[jennyf19]

moving some of the required cache look up to MSAL .NET