Added login flow to get access token

internal/login.go

@@ -0,0 +1,41 @@
+package magellan
+
+import (
+	"fmt"
+	"net/http"
+
+	"github.com/go-chi/chi/v5"
+	"github.com/pkg/browser"
+)
+
+func Login(loginUrl string, targetHost string, targetPort int) (string, error) {
+	var accessToken string
+
+	// check and make sure the login URL isn't empty
+	if loginUrl == "" {
+		return "", fmt.Errorf("no login URL provided")
+	}
+
+	// if a target host and port are provided, then add to URL
+	if targetHost != "" && targetPort > 0 && targetPort < 65536 {
+		loginUrl += fmt.Sprintf("?target=http://%s:%d", targetHost, targetPort)
+	}
+
+	// open browser with the specified URL
+	err := browser.OpenURL(loginUrl)
+	if err != nil {
+		return "", fmt.Errorf("failed to open browser: %v", err)
+	}
+
+	// start a temporary server to listen for token
+	s := http.Server{
+		Addr: fmt.Sprintf("%s:%d", targetHost, targetPort),
+	}
+	r := chi.NewRouter()
+	r.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
+		// try and extract access token from headers
+		accessToken = r.Header.Get("access_token")
+		s.Close()
+	})
+	return accessToken, s.ListenAndServe()
+}