* remote_storage/azure: allow a per-request HTTP client
Thread an optional *http.Client through NewAzBlobClient and add
azure.MakeWithHTTPClient, mirroring the S3 backend. When set, the client
overrides the azblob transport so a caller can pin the dial path. The
existing makers pass nil, so behavior is unchanged.
* volume: extend the remote-endpoint guard to the azure backend
The endpoint validation and rebinding-safe dialer in FetchAndWriteNeedle
covered the S3-SDK backends. The azure backend also dials a caller-supplied
AzureEndpoint, so route both families through a single guardedRemoteClient
helper that returns the endpoint each backend dials and a constructor bound
to the guarded HTTP client. azure is guarded only when AzureEndpoint is set;
an empty endpoint derives the public host from the account.
-volume.allowUntrustedRemoteEndpoints still opts out.
* rust volume: assert the azure endpoint has no remote-client path
The Rust volume server has no azure backend, so make_remote_storage_client
rejects the type before any client is built. Add a regression test pinning
that invariant.
* azure: let the blob endpoint be configured
The service url was always derived as <account>.blob.core.windows.net,
which leaves out Azure Government, Azure China, and private endpoints.
Name the blob service url instead and those accounts become reachable.
The url has to be https, since the account key or the bearer token would
otherwise travel in the clear.
* azure: reject an endpoint that carries no hostname
A url like https://:443/ has a host of ":443", so the emptiness check on
Host let it through and the request only failed once it reached Azure.
The hostname is what has to be there.
* azure: authenticate the blob sink with Entra ID
Shared account keys have to be distributed and rotated everywhere a sink
runs. Leaving account_key empty now falls back to the identity chain, so a
workload identity or managed identity carries the authorization instead.
* azure: authenticate remote storage with Entra ID
The remote storage client demanded an account key and refused to start
without one. Fall back to the identity chain when it is absent, and let
azure.client_id pin a user-assigned identity.
* azure: reject a malformed storage account name
The account name is interpolated into the service URL, so a name carrying
a "/", "?" or "@" moves the authority elsewhere and an authenticated
request follows it. Hold callers to Azure's own naming rule instead.
* azure: keep a leftover environment key off the identity path
A configured client id asks for Entra ID, but AZURE_STORAGE_ACCESS_KEY
still filled in the account key behind it. An old mounted secret would go
on authenticating until it rotated, and the failure then blamed the key.
* azure: say what the identity path reads from the environment
A pinned client id alone is not enough for workload identity: the tenant
and the projected token come from the environment, and missing them only
surfaces later, when a token is first requested.
Chris Lu