provider/azure: adding credential produces error when service principal exists

[Roger Peppe]

I did "juju add-credential azure" and after completing the interaction, saw this error:

 12:31:21 ERROR cmd supercommand.go:458 finalizing credential: ad.ServicePrincipalsClient#Create: Failure responding to request: StatusCode=0 -- Original Error: ad: error response cannot be parsed: "\ufeff{\"odata.error\":{\"code\":\"Request_MultipleObjectsWithSameKeyValue\",\"message\":{\"lang\":\"en\",\"value\":\"Another object with the same value for property servicePrincipalNames already exists.\"},\"requestId\":\"46a97035-e286-4d41-8eee-ae33de2f0288\",\"date\":\"2017-01-18T12:31:21\"}}" error: invalid character 'ï' looking for beginning of value
 12:31:21 DEBUG cmd supercommand.go:459 (error details: [{github.com/juju/juju/cmd/juju/cloud/addcredential.go:244: finalizing credential} {github.com/juju/juju/provider/azure/credentials.go:95: } {github.com/juju/juju/provider/azure/internal/azureauth/interactive.go:164: } {github.com/juju/juju/provider/azure/internal/azureauth/interactive.go:218: } {ad.ServicePrincipalsClient#Create: Failure responding to request: StatusCode=0 -- Original Error: ad: error response cannot be parsed: "\ufeff{\"odata.error\":{\"code\":\"Request_MultipleObjectsWithSameKeyValue\",\"message\":{\"lang\":\"en\",\"value\":\"Another object with the same value for property servicePrincipalNames already exists.\"},\"requestId\":\"46a97035-e286-4d41-8eee-ae33de2f0288\",\"date\":\"2017-01-18T12:31:21\"}}" error: invalid character 'ï' looking for beginning of value}])

It looks like an Azure endpoint is producing a BOM that the client code isn't correctly eliding and so the error isn't correctly diagnosed with isMultipleObjectsWithSameKeyValueErr.

This doesn't always happen (I saw 2 failures in 3 tries). I filed https://github.com/Azure/go-autorest/issues/109 for the underlying bug, but we may be able to work around it in the Juju client code.

[Andrew Wilkins (axwalk)]

https://github.com/juju/juju/pull/6835
https://github.com/juju/juju/pull/6836