Implement ExternalBearerTokenCredentialPolicy in azure-mgmt-core

[jsntcy]

Is your feature request related to a problem? Please describe.
Customer wants to work around #8313 by adding a new custom policy called ExternalBearerTokenCredentialPolicy, but find it difficult.

Describe the solution you'd like
#16519

Describe alternatives you've considered
A clear and concise description of any alternative solutions or features you've considered.

Additional context
Add any other context or screenshots about the feature request here.

[jiasli]

It is not easy to use this policy with Azure CLI dev branch because dev branch uses external_tenant_token_retriever to retrieve tokens for external tenants:

https://github.com/Azure/azure-cli/blob/039fa21db4fdf6dfb22958aaf1c3f614e1fc3b59/src/azure-cli-core/azure/cli/core/adal_authentication.py#L22

    def __init__(self, token_retriever, external_tenant_token_retriever=None):

Adopting this Track 2-compatible policy would require an overhaul of azure-cli-core to switch from external_tenant_token_retriever to external credentials. I prefer not to use this policy for Azure CLI dev, as this will be throw-away code.

Hi @jsntcy. Thank you for opening this issue and giving us the opportunity to assist. We believe that this has been addressed. If you feel that further discussion is needed, please add a comment with the text “/unresolve” to remove the “issue-addressed” label and continue the conversation.

Hi @jsntcy, since you haven’t asked that we “/unresolve” the issue, we’ll close this out. If you believe further discussion is needed, please add a comment “/unresolve” to reopen the issue.