feat(learning-auth): add optional JWT learning flow with secure demo endpoint

src/test/java/com/example/demo/controller/AuthFlowTest.java

@@ -0,0 +1,54 @@
+package com.example.demo.controller;
+
+import com.fasterxml.jackson.databind.ObjectMapper;
+import org.junit.jupiter.api.Test;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.test.autoconfigure.web.servlet.AutoConfigureMockMvc;
+import org.springframework.boot.test.context.SpringBootTest;
+import org.springframework.http.MediaType;
+import org.springframework.test.web.servlet.MockMvc;
+
+import java.util.Map;
+
+import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.get;
+import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.post;
+import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.jsonPath;
+import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.status;
+
+@SpringBootTest
+@AutoConfigureMockMvc
+class AuthFlowTest {
+
+    @Autowired
+    private MockMvc mockMvc;
+
+    @Autowired
+    private ObjectMapper objectMapper;
+
+    @Test
+    void secureEndpointShouldRejectWithoutToken() throws Exception {
+        mockMvc.perform(get("/api/secure/me"))
+                .andExpect(status().isUnauthorized())
+                .andExpect(jsonPath("$.code").value(401));
+    }
+
+    @Test
+    void shouldAccessSecureEndpointWithValidToken() throws Exception {
+        String loginReq = objectMapper.writeValueAsString(Map.of("username", "admin", "password", "admin123"));
+
+        String loginResp = mockMvc.perform(post("/api/auth/login")
+                        .contentType(MediaType.APPLICATION_JSON)
+                        .content(loginReq))
+                .andExpect(status().isOk())
+                .andExpect(jsonPath("$.code").value(0))
+                .andReturn().getResponse().getContentAsString();
+
+        String token = objectMapper.readTree(loginResp).path("data").path("token").asText();
+
+        mockMvc.perform(get("/api/secure/me")
+                        .header("Authorization", "Bearer " + token))
+                .andExpect(status().isOk())
+                .andExpect(jsonPath("$.code").value(0))
+                .andExpect(jsonPath("$.data.principal").value("admin"));
+    }
+}