added azure domain parameter

changelog/unreleased/issue-2468

@@ -0,0 +1,6 @@
+Enhancement: Add support for non-global Azure clouds
+
+Restic backups on azure only worked for storages on the global domain `core.windows.net`. This meant that backups to other domains such as Azure China (`core.chinacloudapi.cn') were not supported. Restic now allows overriding the global domain using the environment variable `AZURE_ENDPOINT_SUFFIX'.
+
+https://github.com/restic/restic/issues/2468
+https://github.com/restic/restic/pull/4387

doc/030_preparing_a_new_repo.rst

@@ -537,6 +537,13 @@ or
     $ export AZURE_ACCOUNT_NAME=<ACCOUNT_NAME>
     $ export AZURE_ACCOUNT_SAS=<SAS_TOKEN>
 
+Restic will use Azure's global domain ``core.windows.net`` by default. You can specify other
+domains to be used like so:
+
+.. code-block:: console
+
+    $export AZURE_ENDPOINT_SUFFIX=<ENDPOINT_SUFFIX>
+
 Afterwards you can initialize a repository in a container called ``foo`` in the
 root path like this:
 

doc/040_backup.rst

@@ -614,6 +614,7 @@ environment variables. The following lists these environment variables:
     AZURE_ACCOUNT_NAME                  Account name for Azure
     AZURE_ACCOUNT_KEY                   Account key for Azure
     AZURE_ACCOUNT_SAS                   Shared access signatures (SAS) for Azure
+    AZURE_ENDPOINT_SUFFIX               Domain of Azure Storage (default: core.windows.net)
 
     GOOGLE_PROJECT_ID                   Project ID for Google Cloud Storage
     GOOGLE_APPLICATION_CREDENTIALS      Application Credentials for Google Cloud Storage (e.g. $HOME/.config/gs-secret-restic-key.json)

internal/backend/azure/azure.go

@@ -53,7 +53,13 @@ func open(cfg Config, rt http.RoundTripper) (*Backend, error) {
 	var client *azContainer.Client
 	var err error
 
-	url := fmt.Sprintf("https://%s.blob.core.windows.net/%s", cfg.AccountName, cfg.Container)
+	var endpointSuffix string
+	if cfg.EndpointSuffix != "" {
+		endpointSuffix = cfg.EndpointSuffix
+	} else {
+		endpointSuffix = "core.windows.net"
+	}
+	url := fmt.Sprintf("https://%s.blob.%s/%s", cfg.AccountName, endpointSuffix, cfg.Container)
 	opts := &azContainer.ClientOptions{
 		ClientOptions: azcore.ClientOptions{
 			Transport: &http.Client{Transport: rt},

internal/backend/azure/config.go

@@ -16,6 +16,7 @@ type Config struct {
 	AccountName    string
 	AccountSAS     options.SecretString
 	AccountKey     options.SecretString
+	EndpointSuffix string
 	Container      string
 	Prefix         string
 
@@ -71,4 +72,7 @@ func (cfg *Config) ApplyEnvironment(prefix string) {
 	if cfg.AccountSAS.String() == "" {
 		cfg.AccountSAS = options.NewSecretString(os.Getenv(prefix + "AZURE_ACCOUNT_SAS"))
 	}
+	if cfg.EndpointSuffix == "" {
+		cfg.EndpointSuffix = os.Getenv("AZURE_ENDPOINT_SUFFIX")
+	}
 }