Incorrect number of segments with auth emulator

[big-wisdom]

Problem

Emulators distribute an unsigned JWT (with only 2 segments) but in auth/token_verifier.go, in verifyToken it returns these unsigned tokens as invalid with the result "incorrect number of segments"

[google-oss-bot]

I found a few problems with this issue:

• I couldn't figure out how to label this issue, so I've labeled it for a human to triage. Hang tight.
• This issue does not seem to follow the issue template. Make sure you provide all the required information.