Validate global config too

Signed-off-by: Friedrich Gonzalez <friedrichg@gmail.com>

pkg/alertmanager/api.go

@@ -432,6 +432,9 @@ func validateReceiverTLSConfig(cfg commoncfg.TLSConfig) error {
 // validateGlobalConfig validates the Global config and returns an error if it contains
 // settings now allowed by Cortex.
 func validateGlobalConfig(cfg config.GlobalConfig) error {
+	if cfg.OpsGenieAPIKeyFile != "" {
+		return errOpsGenieAPIKeyFileNotAllowed
+	}
 	if cfg.SlackAPIURLFile != "" {
 		return errSlackAPIURLFileNotAllowed
 	}

pkg/alertmanager/api_test.go

@@ -371,6 +371,23 @@ alertmanager_config: |
 `,
 			err: errors.Wrap(errOAuth2SecretFileNotAllowed, "error validating Alertmanager config"),
 		},
+		{
+			name: "Should return error if global opsgenie_api_key_file is set",
+			cfg: `
+alertmanager_config: |
+  global:
+    opsgenie_api_key_file: /secrets
+
+  receivers:
+    - name: default-receiver
+      webhook_configs:
+        - url: http://localhost
+
+  route:
+    receiver: 'default-receiver'
+`,
+			err: errors.Wrap(errOpsGenieAPIKeyFileNotAllowed, "error validating Alertmanager config"),
+		},
 		{
 			name: "Should return error if global slack_api_url_file is set",
 			cfg: `