Allow using target app ID directly for GCIR (#223)

Atlassian insists that they need a way to pass the target app directly to GCIR. I don't like supporting this as an official use case of the SDK. So just enable this under the hood

>Ask
Support client initialize response creation by target app parameter (by ID good if ID can be looked up by name) instead of client key.
Currently the target app is looked up by the supplied client key parameter and used to filter the gates, dynamic configs, and layers. We would like to supply the target app directly.
This will ideally reduce the number of client keys required in some cases (i.e. use of kill-switches and configuration where we don’t want to log events in the client) and ease integration with our new Statsig sidecar.
Impact
Streamlining SSR use cases and Feature Flag Service providing dynamic configuration
Fewer client keys required (potentially)

client.go

@@ -298,13 +298,7 @@ func (c *Client) GetClientInitializeResponseImpl(user User, options *GCIROptions
 			return *new(ClientInitializeResponse)
 		}
 		user = normalizeUser(user, *c.options)
-		includeLocalOverrides := options.IncludeLocalOverrides
-		clientKey := options.ClientKey
-		hashAlgorithm := options.HashAlgorithm
-		if hashAlgorithm != "none" && hashAlgorithm != "djb2" {
-			hashAlgorithm = "sha256"
-		}
-		response := c.evaluator.getClientInitializeResponse(user, clientKey, includeLocalOverrides, hashAlgorithm)
+		response := c.evaluator.getClientInitializeResponse(user, options)
 		if response.Time == 0 {
 			c.errorBoundary.logException(errors.New("empty response from server"))
 		}

client_initialize_response.go

@@ -65,10 +65,12 @@ func mergeMaps(a map[string]interface{}, b map[string]interface{}) {
 func getClientInitializeResponse(
 	user User,
 	e *evaluator,
-	clientKey string,
-	includeLocalOverrides bool,
-	hashAlgorithm string,
+	options *GCIROptions,
 ) ClientInitializeResponse {
+	hashAlgorithm := options.HashAlgorithm
+	if hashAlgorithm != "none" && hashAlgorithm != "djb2" {
+		hashAlgorithm = "sha256"
+	}
 	context := StatsigContext{Caller: "getClientInitializeResponse", Hash: hashAlgorithm}
 
 	evalResultToBaseResponse := func(name string, eval *evalResult) (string, baseSpecInitializeResponse) {
@@ -82,7 +84,7 @@ func getClientInitializeResponse(
 	}
 	gateToResponse := func(gateName string, spec configSpec) (string, GateInitializeResponse) {
 		evalRes := &evalResult{}
-		if includeLocalOverrides {
+		if options.IncludeLocalOverrides {
 			if gateOverride, hasOverride := e.getGateOverrideEval(gateName); hasOverride {
 				evalRes = gateOverride
 			} else {
@@ -100,7 +102,7 @@ func getClientInitializeResponse(
 	}
 	configToResponse := func(configName string, spec configSpec) (string, ConfigInitializeResponse) {
 		evalRes := &evalResult{}
-		if includeLocalOverrides {
+		if options.IncludeLocalOverrides {
 			if configOverride, hasOverride := e.getConfigOverrideEval(configName); hasOverride {
 				evalRes = configOverride
 			} else {
@@ -175,7 +177,12 @@ func getClientInitializeResponse(
 		return hashedName, result
 	}
 
-	appId, _ := e.store.getAppIDForSDKKey(clientKey)
+	var appId string
+	if options.TargetAppID != "" {
+		appId = options.TargetAppID
+	} else {
+		appId, _ = e.store.getAppIDForSDKKey(options.ClientKey)
+	}
 	featureGates := make(map[string]GateInitializeResponse)
 	dynamicConfigs := make(map[string]ConfigInitializeResponse)
 	layerConfigs := make(map[string]LayerInitializeResponse)

evaluator.go

@@ -327,8 +327,11 @@ func (e *evaluator) OverrideLayer(layer string, val map[string]interface{}) {
 
 // Gets all evaluated values for the given user.
 // These values can then be given to a Statsig Client SDK via bootstrapping.
-func (e *evaluator) getClientInitializeResponse(user User, clientKey string, includeLocalOverrides bool, hashAlgorithm string) ClientInitializeResponse {
-	return getClientInitializeResponse(user, e, clientKey, includeLocalOverrides, hashAlgorithm)
+func (e *evaluator) getClientInitializeResponse(
+	user User,
+	options *GCIROptions,
+) ClientInitializeResponse {
+	return getClientInitializeResponse(user, e, options)
 }
 
 func (e *evaluator) cleanExposures(exposures []SecondaryExposure, hashAlgorithm string) []SecondaryExposure {

statsig.go

@@ -96,6 +96,7 @@ type Environment struct {
 type GCIROptions struct {
 	IncludeLocalOverrides bool
 	ClientKey             string
+	TargetAppID           string
 	HashAlgorithm         string
 }