✨ feat: implement configuration loading for Casper facilitator

Add functionality to load configuration details for the Casper facilitator in the settler application. This includes default values if the configuration file does not exist, ensuring smoother operation and easier configuration management. Update the `SettlerConfig` struct to include the new fields for facilitator URL and token.

Author: nathfavour

cmd/settler/main.go

@@ -263,6 +263,16 @@ func runProxy(args []string) {
 	}
 	defer udsServer.Close()
 
+	// 3. Load config for Casper facilitator details
+	localCfg, err := config.LoadConfig()
+	if err != nil {
+		log.Printf("⚠️  Could not load local config, using defaults: %v", err)
+		localCfg = &config.SettlerConfig{
+			CasperFacilitatorURL:   "https://x402-facilitator.cspr.cloud",
+			CasperFacilitatorToken: "",
+		}
+	}
+
 	targetURL, err := url.Parse(*target)
 	if err != nil {
 		log.Fatalf("Invalid target URL: %v", err)
@@ -286,11 +296,13 @@ func runProxy(args []string) {
 			ChainID:           parsedChainID,
 			VerifyingContract: common.HexToAddress("0x0000000000000000000000000000000000000000"),
 		},
-		NonceExpiry: 5 * time.Minute,
-		Recipient:   *recipient,
-		Asset:       *asset,
-		Amount:      *amount,
-		DB:          db,
+		NonceExpiry:            5 * time.Minute,
+		Recipient:              *recipient,
+		Asset:                  *asset,
+		Amount:                 *amount,
+		DB:                     db,
+		CasperFacilitatorURL:   localCfg.CasperFacilitatorURL,
+		CasperFacilitatorToken: localCfg.CasperFacilitatorToken,
 	}
 
 	mw := x402.NewMiddleware(cfg)

pkg/config/config.go

@@ -8,10 +8,12 @@ import (
 )
 
 type SettlerConfig struct {
-	RPCURL          string `json:"rpc_url"`
-	PrivateKey      string `json:"private_key"`
-	RegistryAddress string `json:"registry_address"`
-	AgentID         string `json:"agent_id"`
+	RPCURL                 string `json:"rpc_url"`
+	PrivateKey             string `json:"private_key"`
+	RegistryAddress        string `json:"registry_address"`
+	AgentID                string `json:"agent_id"`
+	CasperFacilitatorURL   string `json:"casper_facilitator_url"`
+	CasperFacilitatorToken string `json:"casper_facilitator_token"`
 }
 
 func GetConfigPath() (string, error) {
@@ -33,6 +35,20 @@ func LoadConfig() (*SettlerConfig, error) {
 	}
 	data, err := os.ReadFile(path)
 	if err != nil {
+		if os.IsNotExist(err) {
+			// Auto-initialize default config if it doesn't exist
+			defaultCfg := &SettlerConfig{
+				RPCURL:                 "https://rpc.sepolia.mantle.xyz",
+				RegistryAddress:        "0x33aE8331a2406EEc3A33483001aC5650DA2e0662",
+				AgentID:                "42",
+				CasperFacilitatorURL:   "https://x402-facilitator.cspr.cloud",
+				CasperFacilitatorToken: "", // empty/permissionless default
+			}
+			if err := SaveConfig(defaultCfg); err != nil {
+				return nil, err
+			}
+			return defaultCfg, nil
+		}
 		return nil, err
 	}
 	var cfg SettlerConfig