feat: migrate auth0mock from Node.js to Go

Refactor the application to a Go-based architecture for improved
performance and maintainability. Replace the Dockerfile to utilize a
multi-stage build process, enhancing image efficiency. Implement
comprehensive session store tests to ensure reliability and create
new OAuth handlers for managing authentication efficiently. Update 
documentation to reflect these structural changes.

handlers/session.go

@@ -0,0 +1,97 @@
+package handlers
+
+import (
+	"encoding/json"
+	"log/slog"
+	"net/http"
+
+	"gitlab.com/unboundsoftware/auth0mock/auth"
+	"gitlab.com/unboundsoftware/auth0mock/store"
+)
+
+// SessionHandler handles session-related endpoints
+type SessionHandler struct {
+	jwtService   *auth.JWTService
+	sessionStore *store.SessionStore
+	logger       *slog.Logger
+}
+
+// NewSessionHandler creates a new session handler
+func NewSessionHandler(jwtService *auth.JWTService, sessionStore *store.SessionStore, logger *slog.Logger) *SessionHandler {
+	return &SessionHandler{
+		jwtService:   jwtService,
+		sessionStore: sessionStore,
+		logger:       logger,
+	}
+}
+
+// UserInfo handles GET /userinfo
+func (h *SessionHandler) UserInfo(w http.ResponseWriter, r *http.Request) {
+	w.Header().Set("Content-Type", "application/json")
+	json.NewEncoder(w).Encode(map[string]string{
+		"picture": "https://cdn.playbuzz.com/cdn/5458360f-32ea-460e-a707-1a2d26760558/70bda687-cb84-4756-8a44-8cf735ed87b3.jpg",
+	})
+}
+
+// TokenInfo handles POST /tokeninfo
+func (h *SessionHandler) TokenInfo(w http.ResponseWriter, r *http.Request) {
+	var req struct {
+		IDToken string `json:"id_token"`
+	}
+
+	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
+		http.Error(w, "Invalid request body", http.StatusBadRequest)
+		return
+	}
+
+	if req.IDToken == "" {
+		h.logger.Debug("no token given in body")
+		http.Error(w, "missing id_token", http.StatusUnauthorized)
+		return
+	}
+
+	claims, err := h.jwtService.DecodeToken(req.IDToken)
+	if err != nil {
+		h.logger.Debug("failed to decode token", "error", err)
+		http.Error(w, "invalid id_token", http.StatusUnauthorized)
+		return
+	}
+
+	if userID, ok := claims["sub"].(string); ok {
+		h.logger.Debug("returning token data", "user_id", userID)
+	}
+
+	w.Header().Set("Content-Type", "application/json")
+	json.NewEncoder(w).Encode(claims)
+}
+
+// Logout handles GET /v2/logout
+func (h *SessionHandler) Logout(w http.ResponseWriter, r *http.Request) {
+	returnTo := r.URL.Query().Get("returnTo")
+
+	// Try to get session from cookie
+	cookie, err := r.Cookie("auth0")
+	if err == nil && cookie.Value != "" {
+		h.sessionStore.Delete(cookie.Value)
+		h.logger.Debug("deleted session", "code", cookie.Value)
+	}
+
+	// Clear the cookie
+	http.SetCookie(w, &http.Cookie{
+		Name:     "auth0",
+		Value:    "",
+		Path:     "/",
+		MaxAge:   -1,
+		SameSite: http.SameSiteNoneMode,
+		Secure:   true,
+		HttpOnly: true,
+	})
+
+	if returnTo != "" {
+		http.Redirect(w, r, returnTo, http.StatusFound)
+		return
+	}
+
+	w.WriteHeader(http.StatusOK)
+	w.Write([]byte("Logged out"))
+}