chore: add oauth2 support (#130)

1.add oauth2 server and client example
2.add oauth2 impl in sse
3.add auth doc 
Signed-off-by: jokemanfire <hu.dingyang@zte.com.cn>

examples/servers/templates/mcp_oauth_authorize.html

@@ -0,0 +1,106 @@
+<!DOCTYPE html>
+<html lang="en">
+<head>
+    <meta charset="UTF-8">
+    <meta name="viewport" content="width=device-width, initial-scale=1.0">
+    <title>MCP OAuth</title>
+    <style>
+        :root {
+            --primary-color: #4285f4;
+            --secondary-color: #f1f1f1;
+            --text-color: #333;
+            --border-color: #ddd;
+        }
+
+        body {
+            font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
+            margin: 0;
+            padding: 0;
+            min-height: 100vh;
+            display: flex;
+            align-items: center;
+            justify-content: center;
+            background-color: #f8f9fa;
+            color: var(--text-color);
+        }
+
+        .container {
+            background: white;
+            padding: 2rem;
+            border-radius: 12px;
+            box-shadow: 0 4px 6px rgba(0, 0, 0, 0.1);
+            max-width: 600px;
+            width: 90%;
+            margin: 1rem;
+        }
+
+        h1 {
+            margin: 0 0 1.5rem 0;
+            font-size: 1.8rem;
+            text-align: center;
+        }
+
+        .client-info {
+            background: var(--secondary-color);
+            padding: 1rem;
+            border-radius: 8px;
+            margin-bottom: 1.5rem;
+        }
+
+        .btn-group {
+            display: flex;
+            gap: 1rem;
+            justify-content: center;
+        }
+
+        .btn {
+            padding: 0.75rem 1.5rem;
+            border-radius: 6px;
+            cursor: pointer;
+            font-size: 1rem;
+            transition: all 0.2s;
+            border: none;
+        }
+
+        .btn-primary {
+            background-color: var(--primary-color);
+            color: white;
+        }
+
+        .btn-primary:hover {
+            background-color: #3367d6;
+        }
+
+        .btn-secondary {
+            background-color: var(--secondary-color);
+            color: var(--text-color);
+            border: 1px solid var(--border-color);
+        }
+
+        .btn-secondary:hover {
+            background-color: #e0e0e0;
+        }
+    </style>
+</head>
+<body>
+    <div class="container">
+        <h1>MCP OAuth</h1>
+        <div class="client-info">
+            <p><strong>{{ client_id }}</strong> requests access to your account.</p>
+            <p>requested scopes: {{ scopes }}</p>
+        </div>
+        
+        <form action="/oauth/approve" method="post">
+            <input type="hidden" name="client_id" value="{{ client_id }}">
+            <input type="hidden" name="redirect_uri" value="{{ redirect_uri }}">
+            <input type="hidden" name="scope" value="{{ scope }}">
+            <input type="hidden" name="state" value="{{ state }}">
+            
+            <div class="btn-group">
+                <button type="submit" name="approved" value="true" class="btn btn-primary">Approve</button>
+                <button type="submit" name="approved" value="false" class="btn btn-secondary">Reject</button>
+            </div>
+        </form>
+    </div>
+</body>
+</html>