Add solution for Challenge 5 (#718)

Co-authored-by: go-interview-practice-bot[bot] <230190823+go-interview-practice-bot[bot]@users.noreply.github.com>

Author: iamsurajmandal

challenge-5/submissions/iamsurajmandal/solution-template.go

@@ -0,0 +1,61 @@
+package main
+
+import (
+    "context"
+	"fmt"
+	"net/http"
+)
+
+const validToken = "secret"
+
+// AuthMiddleware checks the "X-Auth-Token" header.
+// If it's "secret", call the next handler.
+// Otherwise, respond with 401 Unauthorized.
+func AuthMiddleware(next http.Handler) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+	    auth := r.Header.Get("X-Auth-Token")
+	    fmt.Println("hey this token",auth)
+	    if (auth == validToken) {
+	        ctx := context.WithValue(r.Context(), validToken, auth)
+		    next.ServeHTTP(w, r.WithContext(ctx)) // calling next handleer
+	    } else {
+	       http.Error(w, "", http.StatusUnauthorized)
+	       return;
+	    }
+		// TODO: Implement the logic:
+		//  1) Grab the "X-Auth-Token" header
+		//  2) Compare against validToken
+		//  3) If mismatch or missing, respond with 401
+		//  4) Otherwise pass to next handler
+	})
+}
+
+// helloHandler returns "Hello!" on GET /hello
+func helloHandler(w http.ResponseWriter, r *http.Request) {
+	fmt.Fprint(w, "Hello!")
+}
+
+// secureHandler returns "You are authorized!" on GET /secure
+func secureHandler(w http.ResponseWriter, r *http.Request) {
+	fmt.Fprint(w, "You are authorized!")
+}
+
+// SetupServer configures the HTTP routes with the authentication middleware.
+func SetupServer() http.Handler {
+	mux := http.NewServeMux()
+
+	// Public route: /hello (no auth required)
+	mux.HandleFunc("/hello", helloHandler)
+
+	// Secure route: /secure
+	// Wrap with AuthMiddleware
+	secureRoute := http.HandlerFunc(secureHandler)
+	mux.Handle("/secure", AuthMiddleware(secureRoute))
+
+	return mux
+}
+
+func main() {
+	// Optional: you can run a real server for local testing
+	// http.ListenAndServe(":8080", SetupServer())
+}