Add support for Azure Blob Storage with Managed Identity

[sandy2008]

Is your feature request related to a problem? Please describe.

• Example: https://docs.microsoft.com/en-us/azure/active-directory/managed-identities-azure-resources/tutorial-linux-vm-access-storage
• We need to add support for Azure Blob Storage with Managed Identity in certain VM not just with access key & account.

Describe the solution you'd like

• Add support for constantly get Bearer Token & get the bulks with the Token.

[sandy2008]

Example:

package main

import (
	"fmt"
	"github.com/Azure/go-autorest/autorest/adal"
)

func main() {
	msiEndpoint, _ := adal.GetMSIVMEndpoint()

	var spt *adal.ServicePrincipalToken
	var err error
	
	var resource string = "https%3A%2F%2Fstorage.azure.com%2F"
	
	spt, err = adal.NewServicePrincipalTokenFromMSI(msiEndpoint, resource)
	
	fmt.Println(spt)
	fmt.Println(err)
}

[stale]

Hi! This issue has been automatically marked as stale because it has not had any
activity in the past 30 days.

We use a stalebot among other tools to help manage the state of issues in this project.
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[tomasfreund]

I'd also like if there was an option to select the managed identity to use by client id. This is required when an AKS cluster has multiple identities, you need to specify which one to use or it fails.

[stale]

Hi! This issue has been automatically marked as stale because it has not had any
activity in the past 30 days.

We use a stalebot among other tools to help manage the state of issues in this project.
A stalebot can be very useful in closing issues in a number of cases; the most common
is closing issues or PRs where the original reporter has not responded.

Stalebots are also emotionless and cruel and can close issues which are still very relevant.

If this issue is important to you, please add a comment to keep it open. More importantly, please add a thumbs-up to the original issue entry.

We regularly sort for closed issues which have a stale label sorted by thumbs up.

We may also:

• Mark issues as revivable if we think it's a valid issue but isn't something we are likely
  to prioritize in the future (the issue will still remain closed).
• Add a keepalive label to silence the stalebot if the issue is very common/popular/important.

We are doing our best to respond, organize, and prioritize all issues but it can be a challenging task,
our sincere apologies if you find yourself at the mercy of the stalebot.

[Ottovsky]

Any chance Loki will get Azure MSI support?

[sandy2008]

Any chance Loki will get Azure MSI support?

Already submitted PR & merged.
#4858

[tomasfreund]

It seems that the PR does not allow to select the managed identity to use. This can cause issues when the cluster has multiple managed identities.

[Ottovsky]

Yes, without ability to define User Assigned ID, it will make it hard to use it together with https://github.com/Azure/aad-pod-identity in the AKS.