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It seems some in the GA4GH community view passports as being provided to the server Clearinghouse by the client, rather than the server Clearinghouse retrieving them from Brokers as proposed above. See:
https://docs.google.com/document/d/1T3uYGS2yZflDbLRbG4uxhi8ICqk9C9xWPmJ0DQpFvDU/edit#heading=h.5atd0vqkj5vq
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