use metadata service to grab JWT token

[sjyang18]

Description

This is a patch to fix the issue I reported in (#297). Reference document is https://docs.microsoft.com/en-us/azure/active-directory/managed-identities-azure-resources/how-to-use-vm-token.

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[warrenzhu25]

I want to try MSI feature, but I got com.microsoft.azure.servicebus.primitives.ServiceBusException: Error{condition=amqp:connection:framing-error, description='connection aborted', info=null}. I used 1.2.8. Want to confirm which version should I use? Is there some log I can search for to determine whether MSI took effect?

[sjyang18]

Definitely, 1.2.8 does not include my patch and I verified that.
My patch was merged into dev, and eventually in the master branch, but it doesn't seem to be included in the latest release.

https://github.com/Azure/azure-service-bus-java/blob/master/azure-servicebus/src/main/java/com/microsoft/azure/servicebus/security/ManagedServiceIdentityTokenProvider.java

I will contact the team and let them know.
Meanwhile, you may checkout and build the master branch locally, and try out.
Or, you may checkout my workaround (https://github.com/sjyang18/ServiceBusWithManagedIdentity) with 1.2.8.