feat(core): implement HTTP authentication support for A2A remote agents (#20510)

Co-authored-by: Adam Weidman <adamfweidman@google.com>

packages/core/src/agents/agentLoader.test.ts

@@ -439,6 +439,54 @@ auth:
       });
     });
 
+    it('should parse remote agent with Digest via raw value', async () => {
+      const filePath = await writeAgentMarkdown(`---
+kind: remote
+name: digest-agent
+agent_card_url: https://example.com/card
+auth:
+  type: http
+  scheme: Digest
+  value: username="admin", response="abc123"
+---
+`);
+      const result = await parseAgentMarkdown(filePath);
+      expect(result).toHaveLength(1);
+      expect(result[0]).toMatchObject({
+        kind: 'remote',
+        name: 'digest-agent',
+        auth: {
+          type: 'http',
+          scheme: 'Digest',
+          value: 'username="admin", response="abc123"',
+        },
+      });
+    });
+
+    it('should parse remote agent with generic raw auth value', async () => {
+      const filePath = await writeAgentMarkdown(`---
+kind: remote
+name: raw-agent
+agent_card_url: https://example.com/card
+auth:
+  type: http
+  scheme: CustomScheme
+  value: raw-token-value
+---
+`);
+      const result = await parseAgentMarkdown(filePath);
+      expect(result).toHaveLength(1);
+      expect(result[0]).toMatchObject({
+        kind: 'remote',
+        name: 'raw-agent',
+        auth: {
+          type: 'http',
+          scheme: 'CustomScheme',
+          value: 'raw-token-value',
+        },
+      });
+    });
+
     it('should throw error for Bearer auth without token', async () => {
       const filePath = await writeAgentMarkdown(`---
 kind: remote