Add username from env mysql scaler

CHANGELOG.md

@@ -77,6 +77,7 @@ Here is an overview of all new **experimental** features:
 - **GCP Scalers**: Added custom time horizon in GCP scalers ([#5778](https://github.com/kedacore/keda/issues/5778))
 - **GitHub Scaler**: Fixed pagination, fetching repository list ([#5738](https://github.com/kedacore/keda/issues/5738))
 - **Kafka**: Fix logic to scale to zero on invalid offset even with earliest offsetResetPolicy ([#5689](https://github.com/kedacore/keda/issues/5689))
+- **MYSQL Scaler**: Add support to fetch username from env ([#5883](https://github.com/kedacore/keda/issues/5883))
 
 ### Fixes
 

pkg/scalers/mysql_scaler.go

@@ -115,7 +115,7 @@ func parseMySQLMetadata(config *scalersconfig.ScalerConfig) (*mySQLMetadata, err
 		}
 		meta.port = port
 
-		username, err := GetFromAuthOrMeta(config, "username")
+		username, err := GetFromAuthOrMetaOrEnv(config, "username", "usernameFromEnv")
 		if err != nil {
 			return nil, err
 		}

pkg/scalers/mysql_scaler_test.go

@@ -7,6 +7,7 @@ import (
 )
 
 var testMySQLResolvedEnv = map[string]string{
+	"MYSQL_USERNAME": "test_username",
 	"MYSQL_PASSWORD": "pass",
 	"MYSQL_CONN_STR": "user@tcp(http://my.mysql.dev:3306)/stats_db",
 }
@@ -46,6 +47,13 @@ var testMySQLMetadata = []parseMySQLMetadataTestData{
 		resolvedEnv: testMySQLResolvedEnv,
 		raisesError: false,
 	},
+	// Params instead of conn str with userFromEnv
+	{
+		metadata:    map[string]string{"query": "query", "queryValue": "12", "host": "test_host", "port": "test_port", "usernameFromEnv": "MYSQL_USERNAME", "passwordFromEnv": "MYSQL_PASSWORD", "dbName": "test_dbname"},
+		authParams:  map[string]string{},
+		resolvedEnv: testMySQLResolvedEnv,
+		raisesError: false,
+	},
 	// Params from trigger authentication
 	{
 		metadata:    map[string]string{"query": "query", "queryValue": "12"},
@@ -60,6 +68,13 @@ var testMySQLMetadata = []parseMySQLMetadataTestData{
 		resolvedEnv: testMySQLResolvedEnv,
 		raisesError: true,
 	},
+	// No username provided in authParams, metadata, resolvedEnv
+	{
+		metadata:    map[string]string{"query": "query", "queryValue": "12", "activationQueryValue": "AA"},
+		authParams:  map[string]string{"host": "test_host", "port": "test_port", "password": "MYSQL_PASSWORD", "dbName": "test_dbname"},
+		resolvedEnv: map[string]string{},
+		raisesError: true,
+	},
 }
 
 var mySQLMetricIdentifiers = []mySQLMetricIdentifier{

pkg/scalers/scaler.go

@@ -86,6 +86,24 @@
 	return result, err
 }
 
+// GetFromAuthOrMetaOrEnv helps to get a field from Auth or Meta or Env sections
+func GetFromAuthOrMetaOrEnv(config *scalersconfig.ScalerConfig, field string, envField string) (string, error) {
+	var result string
+	var err error
+	switch {
+	case config.AuthParams[field] != "":
+		return config.AuthParams[field], err
+	case config.TriggerMetadata[field] != "":
+		return config.TriggerMetadata[field], err
+	case config.ResolvedEnv[config.TriggerMetadata[envField]] != "":
+		return config.TriggerMetadata[envField], err
+	}
+	if result == "" {
+		err = fmt.Errorf("%w: no %s or %s given", ErrScalerConfigMissingField, field, envField)
+	}
+	return result, err
+}
+
 // GenerateMetricNameWithIndex helps to add the index prefix to the metric name
 func GenerateMetricNameWithIndex(triggerIndex int, metricName string) string {
 	return fmt.Sprintf("s%d-%s", triggerIndex, metricName)