Concurrent transaction error while logging in

[mbarkley]

We have automated tests that run using a small set of test users. When two instances of the tests are running simultaneously, they will sometimes fail to login this this error:

{"code":13,"message":"datastore: concurrent transaction"}

That error message is returned in the response for the last request in this series of redirects (that happens after successfully logging in through a connected IDP):

Step #2 - "run_journey_test": 	https://identity-concentrator.staging.dnastack.com/identity/loggedin?code=eyJhbGciOiJIUzI1NiJ9.eyJ0b2tlbktpbmQiOiJjb2RlIiwic3ViIjoiMjE1ODViZjQtM2VmMS00MTY4LWIyZWMtYWE2YWVlOTcyZTU5IiwiYXVkIjoiW10iLCJhenAiOiJkZGU3YzAyMS1kZjc0LTQyOWEtYmYwNC0yYmNkYjZiMGJkZmIiLCJzY29wZSI6InByb2ZpbGUgZ2E0Z2hfcGFzc3BvcnRfdjEgZW1haWwgaWRlbnRpdGllcyBvcGVuaWQiLCJleHAiOjE1OTczNTU4OTQsImlhdCI6MTU5NzM1NTI5NH0.Y9kbbQWaQVvC2ZkX-HlyiomOfoE4oB1VWA46_K-uH60&state=66574932-2180-45f5-bc64-4218aba13a54
Step #2 - "run_journey_test": 	https://identity-concentrator.staging.dnastack.com/identity/v1alpha/master/loggedin/wallet?code=eyJhbGciOiJIUzI1NiJ9.eyJ0b2tlbktpbmQiOiJjb2RlIiwic3ViIjoiMjE1ODViZjQtM2VmMS00MTY4LWIyZWMtYWE2YWVlOTcyZTU5IiwiYXVkIjoiW10iLCJhenAiOiJkZGU3YzAyMS1kZjc0LTQyOWEtYmYwNC0yYmNkYjZiMGJkZmIiLCJzY29wZSI6InByb2ZpbGUgZ2E0Z2hfcGFzc3BvcnRfdjEgZW1haWwgaWRlbnRpdGllcyBvcGVuaWQiLCJleHAiOjE1OTczNTU4OTQsImlhdCI6MTU5NzM1NTI5NH0.Y9kbbQWaQVvC2ZkX-HlyiomOfoE4oB1VWA46_K-uH60&state=66574932-2180-45f5-bc64-4218aba13a54

I suspect that this is timing issue where two of our tests are logging in as the same user at the same time. Although this is not likely to cause errors for real users, it would be appreciated if the IC could support simultaneous logins from the same user.