feat: allow getting authorizer from existing file settings (#709)

* feat: allow getting authorizer from existing file settings

Signed-off-by: Tareq Sharafy <tareq.sha@gmail.com>

* fix test

Signed-off-by: Tareq Sharafy <tareq.sha@gmail.com>
Co-authored-by: Joel Hendrix <jhendrix@microsoft.com>

Author: tareksha

autorest/azure/auth/auth.go

@@ -250,6 +250,17 @@ func NewAuthorizerFromFile(resourceBaseURI string) (autorest.Authorizer, error)
 	if err != nil {
 		return nil, err
 	}
+	return settings.GetAuthorizer(resourceBaseURI)
+}
+
+// GetAuthorizer create an Authorizer in the following order.
+// 1. Client credentials
+// 2. Client certificate
+// resourceBaseURI - used to determine the resource type
+func (settings FileSettings) GetAuthorizer(resourceBaseURI string) (autorest.Authorizer, error) {
+	if resourceBaseURI == "" {
+		resourceBaseURI = azure.PublicCloud.ServiceManagementEndpoint
+	}
 	if a, err := settings.ClientCredentialsAuthorizer(resourceBaseURI); err == nil {
 		return a, err
 	}

autorest/azure/auth/auth_test.go

@@ -268,6 +268,26 @@ func TestFileClientCertificateAuthorizer(t *testing.T) {
 	}
 }
 
+func TestFileGetAuthorizerClientCert(t *testing.T) {
+	t.Setenv("AZURE_AUTH_LOCATION", "./testdata/credsutf8.json")
+	settings, err := GetSettingsFromFile()
+	if err != nil {
+		t.Logf("failed to load file settings: %v", err)
+		t.Fail()
+	}
+	// add certificate settings
+	settings.Values[CertificatePath] = "~/fake/path/cert.pfx"
+	settings.Values[CertificatePassword] = "fake-password"
+	auth, err := settings.GetAuthorizer("https://management.azure.com")
+	if err != nil {
+		t.Logf("failed to get authorizer: %v", err)
+		t.Fail()
+	}
+	if _, ok := auth.(*autorest.BearerAuthorizer); !ok {
+		t.Fatalf("unexpected authorizer type %T", auth)
+	}
+}
+
 func TestMultitenantClientCredentials(t *testing.T) {
 	setDefaultEnv()
 	os.Setenv(AuxiliaryTenantIDs, "aux-tenant-1;aux-tenant-2;aux-tenant3")