If you land on an Azure VM with a managed identity, the Instance Metadata Service hands out an access token for the asking:
curl -s -H "Metadata: true" \
"http://169.254.169.254/metadata/identity/oauth2/token?api-version=2018-02-01&resource=https://management.azure.com/" \
| jq -r .access_token
The address 169.254.169.254 is link-local and unroutable — which is exactly
why blocking egress to it from workloads that don’t need it is such a cheap
control. Most don’t.