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LTI user_id uniqueness

LTI user_id uniqueness

Hello,

I tried to conclude the uniquness requirements of the user_id property from the LTI 1.1 spec, but I'm not sure I have a definite answer.

To phrase my question shortly, please indicate which of the following statements is true:

1. A user_id value has to be globally unique.

2. The combination of a user_id and tool_consumer_instance_guid has to be globally unique.

3. The combination of a user_id and oauth_consumer_key has to be globally unique.

Thanks,

Lior