Support both azid and autorest certificate env vars

For certificate authentication, autorest uses the `AZURE_CERTIFICATE_`
prefix whereas azidentity uses `AZURE_CLIENT_CERTIFICATE_`. Let's make
sure the latter is set to the value of the former so as not to break
upgrades.

azure/scope/clients.go

@@ -122,6 +122,16 @@ func (c *AzureClients) setCredentials(subscriptionID, environmentName string) er
 				Cloud: config,
 			},
 		}
+
+		// azidentity uses different envvars for certificate authentication
+		// Let's set it according to the envvars used by autorest, in case they are present
+		_, azidSet := os.LookupEnv("AZURE_CLIENT_CERTIFICATE_PATH")
+		path, autorestSet := os.LookupEnv("AZURE_CERTIFICATE_PATH")
+		if !azidSet && autorestSet {
+			os.Setenv("AZURE_CLIENT_CERTIFICATE_PATH", path)
+			os.Setenv("AZURE_CLIENT_CERTIFICATE_PASSWORD", os.Getenv("AZURE_CERTIFICATE_PASSWORD"))
+		}
+
 		cred, err := azidentity.NewDefaultAzureCredential(&options)
 		if err != nil {
 			return err

test/e2e/common.go

@@ -223,6 +223,16 @@ func GetAuthorizer(settings auth.EnvironmentSettings) (autorest.Authorizer, erro
 			Cloud: config,
 		},
 	}
+
+	// azidentity uses different envvars for certificate authentication
+	// Let's set it according to the envvars used by autorest, in case they are present
+	_, azidSet := os.LookupEnv("AZURE_CLIENT_CERTIFICATE_PATH")
+	path, autorestSet := os.LookupEnv("AZURE_CERTIFICATE_PATH")
+	if !azidSet && autorestSet {
+		os.Setenv("AZURE_CLIENT_CERTIFICATE_PATH", path)
+		os.Setenv("AZURE_CLIENT_CERTIFICATE_PASSWORD", os.Getenv("AZURE_CERTIFICATE_PASSWORD"))
+	}
+
 	cred, err := azidentity.NewDefaultAzureCredential(&options)
 	if err != nil {
 		return nil, err