Hi Marcia,
For me the best is to agree with them how they would like to measure these, but I understand you want to get there with many ideas as possible. As mentioned, the best option for this is to ask PMs involved in other projects, so I hope they gave you already some ideas
For the objectives you mentioned above, there is one which is more clearer:
- Enhance user productivity and experience: Could be measured in terms of time (productivity), which can be measured on how many time it took for users to authenticate before, how many times, etc, and compare with the same data collected after the implementation, and satisfaction (experience), which could be gathered by surveys after the implementation.
For the Open standards support, Centralized session management, and Protection against unauthorized access, you will have to check with PMs to see how they measure this in other projects, however I only can think of comparing before with after, so how many authentication methods they had, and how they have now, etc. But, again, the best is to agree with them how they want to measure this, in a reasonable way.
I hope it helps, but this really should be checked with PMs