[Bug] Add retries on 500/429 errors while fetching for auth token

[devaradhanm]

The sdk doesnt seem to have retry on failure response(https://github.com/Azure/ms-rest-nodeauth/blob/adea8415de97a8076006fbd9948123d09dfdd78d/lib/credentials/msiAppServiceTokenCredentials.ts#L94). So we may need to add retry & caching, make class singleton for results returned by CredentialsProvider.

Refer https://docs.microsoft.com/en-us/azure/active-directory/managed-identities-azure-resources/how-to-use-vm-token#error-handling

Currently, in Azure function sometimes, we have received the below error in production:
Result: Failure

Exception: Error: MSI: Failed to retrieve a token from "http://127.0.0.1:41709/MSI/token/?resource=https%3A%2F%2Fvault.azure.net&api-version=2017-09-01" with an error: {"ExceptionMessage":"","ErrorCode":"service_unavailable","ServiceErrorCodes":null,"StatusCode":503,"Message":null,"CorrelationId":"8b0bb15d-11f7-4a3b-8fbb-3a55ca98a884"}
Stack: Error: MSI: Failed to retrieve a token from "http://127.0.0.1:41709/MSI/token/?resource=https%3A%2F%2Fvault.azure.net&api-version=2017-09-01" with an error: {"ExceptionMessage":"","ErrorCode":"service_unavailable","ServiceErrorCodes":null,"StatusCode":503,"Message":null,"CorrelationId":"8b0bb15d-11f7-4a3b-8fbb-3a55ca98a884"}
    at MSIAppServiceTokenCredentials.<anonymous> (D:\home\site\wwwroot\get-report-func\index.js:56446:23)
    at Generator.next (<anonymous>)
    at fulfilled (D:\home\site\wwwroot\get-report-func\index.js:56384:58)
    at process._tickCallback (internal/process/next_tick.js:68:7)

Area

• Install script
• Update script
• Service

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Expected behavior

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Additional context

[ghost]

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