feat(backend): fail on unknown keys in the config file

cmd/karma/tests/testscript/022_auth_basicAuth_no_credentials.txt

@@ -11,4 +11,4 @@ alertmanager:
 authentication:
   basicAuth:
     users:
-      - foo: bar
+      - username: bar

cmd/karma/tests/testscript/075_config_extra_fileds.txt

@@ -0,0 +1,26 @@
+# Raises an error if --config.file points to a file that contains unknown keys
+karma.bin-should-fail --log.format=text --log.config=false --check-config
+! stdout .
+! stderr 'msg="Configuration is valid"'
+stderr 'msg="Failed to parse configuration file \\"karma.yaml\\": yaml: unmarshal errors:\\n  line 5: field authorizationFoo not found in type config.configSchema"'
+
+-- karma.yaml --
+authentication:
+  header:
+    name: "X-User"
+    value_re: "(.+)"
+authorizationFoo:
+  groups:
+    - name: admins
+      members:
+        - alice
+        - bob
+    - name: users
+      members:
+        - john
+  acl:
+    silences: acl.yaml
+alertmanager:
+  servers:
+    - name: default
+      uri: https://localhost:9093

internal/config/config.go

@@ -4,6 +4,7 @@ import (
 	"bufio"
 	"bytes"
 	"fmt"
+	"io/ioutil"
 	"os"
 	"strings"
 	"time"
@@ -123,6 +124,21 @@ func SetupFlags(f *pflag.FlagSet) {
 	f.String("ui.collapseGroups", "collapsedOnMobile", "Default state for alert groups")
 }
 
+func validateConfigFile(path string) error {
+	f, err := ioutil.ReadFile(path)
+	if err != nil {
+		return err
+	}
+
+	cfg := configSchema{}
+	err = yaml.UnmarshalStrict(f, &cfg)
+	if err != nil {
+		return err
+	}
+
+	return nil
+}
+
 func readConfigFile(k *koanf.Koanf, flags *pflag.FlagSet) (string, error) {
 	var configFile string
 
@@ -243,6 +259,12 @@ func (config *configSchema) Read(flags *pflag.FlagSet) (string, error) {
 		return "", fmt.Errorf("Failed to unmarshal configuration: %v", err)
 	}
 
+	if configFileUsed != "" {
+		if err := validateConfigFile(configFileUsed); err != nil {
+			return "", fmt.Errorf("Failed to parse configuration file %q: %v", configFileUsed, err)
+		}
+	}
+
 	if config.Authentication.Header.Name != "" && len(config.Authentication.BasicAuth.Users) > 0 {
 		return "", fmt.Errorf("Both authentication.basicAuth.users and authentication.header.name is set, only one can be enabled")
 	}

internal/config/config_test.go

@@ -330,3 +330,10 @@ func TestDefaultConfig(t *testing.T) {
 		t.Errorf("Wrong silence form config returned (-want +got):\n%s", diff)
 	}
 }
+
+func TestValidateConfigMissingFile(t *testing.T) {
+	err := validateConfigFile(("/foo/bar/xxx/yyy.yaml"))
+	if err == nil {
+		t.Errorf("validateConfigFile didn't return any error")
+	}
+}