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/clients/Cargo.toml

@@ -11,7 +11,8 @@ rmcp = { path = "../../crates/rmcp", features = [
     "client",
     "transport-sse",
     "transport-child-process",
-    "tower"
+    "tower",
+    "auth"
 ] }
 tokio = { version = "1", features = ["full"] }
 serde = { version = "1.0", features = ["derive"] }
@@ -21,8 +22,9 @@ tracing-subscriber = { version = "0.3", features = ["env-filter"] }
 rand = "0.8"
 futures = "0.3"
 anyhow = "1.0"
-
+url = "2.4"
 tower = "0.5"
+axum = "0.8"
 
 [[example]]
 name = "clients_sse"
@@ -40,3 +42,6 @@ path = "src/everything_stdio.rs"
 name = "clients_collection"
 path = "src/collection.rs"
 
+[[example]]
+name = "oauth_client"
+path = "src/oauth_client.rs"