feat(unstable): initial implementation for the logout method capability

Cargo.toml

@@ -17,6 +17,7 @@ include = ["/src/**/*.rs", "/README.md", "/LICENSE", "/Cargo.toml"]
 unstable = [
     "unstable_auth_methods",
     "unstable_cancel_request",
+    "unstable_logout",
     "unstable_session_fork",
     "unstable_session_model",
     "unstable_session_resume",
@@ -27,6 +28,7 @@ unstable = [
 ]
 unstable_auth_methods = []
 unstable_cancel_request = []
+unstable_logout = []
 unstable_session_fork = []
 unstable_session_model = []
 unstable_session_resume = []

docs/protocol/draft/schema.mdx

@@ -135,7 +135,7 @@ See protocol docs: [Extensibility](https://agentclientprotocol.com/protocol/exte
 <ResponseField name="agentCapabilities" type={<a href="#agentcapabilities">AgentCapabilities</a>} >
   Capabilities supported by the agent.
 
-    - Default: `{"loadSession":false,"mcpCapabilities":{"http":false,"sse":false},"promptCapabilities":{"audio":false,"embeddedContext":false,"image":false},"sessionCapabilities":{}}`
+    - Default: `{"auth":{},"loadSession":false,"mcpCapabilities":{"http":false,"sse":false},"promptCapabilities":{"audio":false,"embeddedContext":false,"image":false},"sessionCapabilities":{}}`
 
 </ResponseField>
 <ResponseField name="agentInfo" type={<><span><a href="#implementation">Implementation</a></span><span> | null</span></>} >
@@ -158,6 +158,61 @@ The client should disconnect, if it doesn't support this version.
 
 </ResponseField>
 
+### <span class="font-mono">logout</span>
+
+**UNSTABLE**
+
+This capability is not part of the spec yet, and may be removed or changed at any point.
+
+Logs out of the current authenticated state.
+
+After a successful logout, all new sessions will require authentication.
+There is no guarantee about the behavior of already running sessions.
+
+#### <span class="font-mono">LogoutRequest</span>
+
+**UNSTABLE**
+
+This capability is not part of the spec yet, and may be removed or changed at any point.
+
+Request parameters for the logout method.
+
+Terminates the current authenticated session.
+
+**Type:** Object
+
+**Properties:**
+
+<ResponseField name="_meta" type={"object | null"} >
+  The _meta property is reserved by ACP to allow clients and agents to attach additional
+metadata to their interactions. Implementations MUST NOT make assumptions about values at
+these keys.
+
+See protocol docs: [Extensibility](https://agentclientprotocol.com/protocol/extensibility)
+
+</ResponseField>
+
+#### <span class="font-mono">LogoutResponse</span>
+
+**UNSTABLE**
+
+This capability is not part of the spec yet, and may be removed or changed at any point.
+
+Response to the `logout` method.
+
+**Type:** Object
+
+**Properties:**
+
+<ResponseField name="_meta" type={"object | null"} >
+  The _meta property is reserved by ACP to allow clients and agents to attach additional
+metadata to their interactions. Implementations MUST NOT make assumptions about values at
+these keys.
+
+See protocol docs: [Extensibility](https://agentclientprotocol.com/protocol/extensibility)
+
+</ResponseField>
+
 <a id="session-cancel"></a>
 ### <span class="font-mono">session/cancel</span>
 
@@ -1555,6 +1610,33 @@ See protocol docs: [Extensibility](https://agentclientprotocol.com/protocol/exte
   The ID of the request to cancel.
 </ResponseField>
 
+## <span class="font-mono">AgentAuthCapabilities</span>
+
+**UNSTABLE**
+
+This capability is not part of the spec yet, and may be removed or changed at any point.
+
+Authentication-related capabilities supported by the agent.
+
+**Type:** Object
+
+**Properties:**
+
+<ResponseField name="_meta" type={"object | null"} >
+  The _meta property is reserved by ACP to allow clients and agents to attach additional
+metadata to their interactions. Implementations MUST NOT make assumptions about values at
+these keys.
+
+See protocol docs: [Extensibility](https://agentclientprotocol.com/protocol/extensibility)
+
+</ResponseField>
+<ResponseField name="logout" type={<><span><a href="#logoutcapabilities">LogoutCapabilities</a></span><span> | null</span></>} >
+  Whether the agent supports the logout method.
+
+By supplying `\{\}` it means that the agent supports the logout method.
+
+</ResponseField>
+
 ## <span class="font-mono">AgentCapabilities</span>
 
 Capabilities supported by the agent.
@@ -1575,6 +1657,16 @@ these keys.
 
 See protocol docs: [Extensibility](https://agentclientprotocol.com/protocol/extensibility)
 
+</ResponseField>
+<ResponseField name="auth" type={<a href="#agentauthcapabilities">AgentAuthCapabilities</a>} >
+  **UNSTABLE**
+
+This capability is not part of the spec yet, and may be removed or changed at any point.
+
+Authentication-related capabilities supported by the agent.
+
+    - Default: `{}`
+
 </ResponseField>
 <ResponseField name="loadSession" type={"boolean"} >
   Whether the agent supports `session/load`.
@@ -2706,6 +2798,29 @@ If not provided, the name should be used for display.
 for debugging or metrics purposes. (e.g. "1.0.0").
 </ResponseField>
 
+## <span class="font-mono">LogoutCapabilities</span>
+
+**UNSTABLE**
+
+This capability is not part of the spec yet, and may be removed or changed at any point.
+
+Logout capabilities supported by the agent.
+
+By supplying `\{\}` it means that the agent supports the logout method.
+
+**Type:** Object
+
+**Properties:**
+
+<ResponseField name="_meta" type={"object | null"} >
+  The _meta property is reserved by ACP to allow clients and agents to attach additional
+metadata to their interactions. Implementations MUST NOT make assumptions about values at
+these keys.
+
+See protocol docs: [Extensibility](https://agentclientprotocol.com/protocol/extensibility)
+
+</ResponseField>
+
 ## <span class="font-mono">McpCapabilities</span>
 
 MCP capabilities supported by the agent

docs/rfds/logout-method.mdx

@@ -66,22 +66,27 @@ interface LogoutResponse {
 
 ### Capability Advertisement
 
-The `logout` capability should be advertised within a new `authCapabilities` object in `AgentCapabilities`:
+The `logout` capability should be advertised within a new `auth` object in `AgentCapabilities`:
 
 ```typescript
 interface AgentCapabilities {
   // ... existing fields ...
 
   /** Authentication-related capabilities */
-  authCapabilities?: AuthCapabilities;
+  auth?: AgentAuthCapabilities;
 }
 
-interface AuthCapabilities {
+interface AgentAuthCapabilities {
   /** Extension metadata */
   _meta?: Record<string, unknown>;
 
-  /** Agent supports the logout method */
-  logout?: boolean;
+  /** Agent supports the logout method. Supply `{}` to indicate support. */
+  logout?: LogoutCapabilities;
+}
+
+interface LogoutCapabilities {
+  /** Extension metadata */
+  _meta?: Record<string, unknown>;
 }
 ```
 
@@ -90,17 +95,30 @@ interface AuthCapabilities {
 ```json
 {
   "$defs": {
-    "AuthCapabilities": {
+    "AgentAuthCapabilities": {
       "description": "Authentication-related capabilities supported by the agent.",
       "properties": {
         "_meta": {
           "additionalProperties": true,
           "type": ["object", "null"]
         },
         "logout": {
-          "type": "boolean",
-          "default": false,
-          "description": "Whether the agent supports the logout method."
+          "allOf": [
+            {
+              "$ref": "#/$defs/LogoutCapabilities"
+            }
+          ],
+          "description": "Whether the agent supports the logout method. Supply `{}` to indicate support."
+        }
+      },
+      "type": "object"
+    },
+    "LogoutCapabilities": {
+      "description": "Logout capabilities supported by the agent. Supply `{}` to indicate support.",
+      "properties": {
+        "_meta": {
+          "additionalProperties": true,
+          "type": ["object", "null"]
         }
       },
       "type": "object"
@@ -159,7 +177,7 @@ interface AuthCapabilities {
 ### Behavior
 
 1. **Pre-condition**: The client should only call `logout` if:
-   - The agent advertises `authCapabilities.logout: true`
+   - The agent advertises `auth.logout: {}`
 
 2. **Agent responsibilities**:
    - Invalidate any stored tokens or credentials as appropriate

schema/meta.unstable.json

@@ -2,6 +2,7 @@
   "agentMethods": {
     "authenticate": "authenticate",
     "initialize": "initialize",
+    "logout": "logout",
     "session_cancel": "session/cancel",
     "session_close": "session/close",
     "session_fork": "session/fork",

schema/schema.unstable.json

@@ -1,5 +1,27 @@
 {
   "$defs": {
+    "AgentAuthCapabilities": {
+      "description": "**UNSTABLE**\n\nThis capability is not part of the spec yet, and may be removed or changed at any point.\n\nAuthentication-related capabilities supported by the agent.",
+      "properties": {
+        "_meta": {
+          "additionalProperties": true,
+          "description": "The _meta property is reserved by ACP to allow clients and agents to attach additional\nmetadata to their interactions. Implementations MUST NOT make assumptions about values at\nthese keys.\n\nSee protocol docs: [Extensibility](https://agentclientprotocol.com/protocol/extensibility)",
+          "type": ["object", "null"]
+        },
+        "logout": {
+          "anyOf": [
+            {
+              "$ref": "#/$defs/LogoutCapabilities"
+            },
+            {
+              "type": "null"
+            }
+          ],
+          "description": "Whether the agent supports the logout method.\n\nBy supplying `{}` it means that the agent supports the logout method."
+        }
+      },
+      "type": "object"
+    },
     "AgentCapabilities": {
       "description": "Capabilities supported by the agent.\n\nAdvertised during initialization to inform the client about\navailable features and content types.\n\nSee protocol docs: [Agent Capabilities](https://agentclientprotocol.com/protocol/initialization#agent-capabilities)",
       "properties": {
@@ -8,6 +30,15 @@
           "description": "The _meta property is reserved by ACP to allow clients and agents to attach additional\nmetadata to their interactions. Implementations MUST NOT make assumptions about values at\nthese keys.\n\nSee protocol docs: [Extensibility](https://agentclientprotocol.com/protocol/extensibility)",
           "type": ["object", "null"]
         },
+        "auth": {
+          "allOf": [
+            {
+              "$ref": "#/$defs/AgentAuthCapabilities"
+            }
+          ],
+          "default": {},
+          "description": "**UNSTABLE**\n\nThis capability is not part of the spec yet, and may be removed or changed at any point.\n\nAuthentication-related capabilities supported by the agent."
+        },
         "loadSession": {
           "default": false,
           "description": "Whether the agent supports `session/load`.",
@@ -220,6 +251,14 @@
                   ],
                   "title": "AuthenticateResponse"
                 },
+                {
+                  "allOf": [
+                    {
+                      "$ref": "#/$defs/LogoutResponse"
+                    }
+                  ],
+                  "title": "LogoutResponse"
+                },
                 {
                   "allOf": [
                     {
@@ -842,6 +881,15 @@
                   "description": "Authenticates the client using the specified authentication method.\n\nCalled when the agent requires authentication before allowing session creation.\nThe client provides the authentication method ID that was advertised during initialization.\n\nAfter successful authentication, the client can proceed to create sessions with\n`new_session` without receiving an `auth_required` error.\n\nSee protocol docs: [Initialization](https://agentclientprotocol.com/protocol/initialization)",
                   "title": "AuthenticateRequest"
                 },
+                {
+                  "allOf": [
+                    {
+                      "$ref": "#/$defs/LogoutRequest"
+                    }
+                  ],
+                  "description": "**UNSTABLE**\n\nThis capability is not part of the spec yet, and may be removed or changed at any point.\n\nLogs out of the current authenticated state.\n\nAfter a successful logout, all new sessions will require authentication.\nThere is no guarantee about the behavior of already running sessions.",
+                  "title": "LogoutRequest"
+                },
                 {
                   "allOf": [
                     {
@@ -1783,6 +1831,7 @@
             }
           ],
           "default": {
+            "auth": {},
             "loadSession": false,
             "mcpCapabilities": {
               "http": false,
@@ -1990,6 +2039,43 @@
       "x-method": "session/load",
       "x-side": "agent"
     },
+    "LogoutCapabilities": {
+      "description": "**UNSTABLE**\n\nThis capability is not part of the spec yet, and may be removed or changed at any point.\n\nLogout capabilities supported by the agent.\n\nBy supplying `{}` it means that the agent supports the logout method.",
+      "properties": {
+        "_meta": {
+          "additionalProperties": true,
+          "description": "The _meta property is reserved by ACP to allow clients and agents to attach additional\nmetadata to their interactions. Implementations MUST NOT make assumptions about values at\nthese keys.\n\nSee protocol docs: [Extensibility](https://agentclientprotocol.com/protocol/extensibility)",
+          "type": ["object", "null"]
+        }
+      },
+      "type": "object"
+    },
+    "LogoutRequest": {
+      "description": "**UNSTABLE**\n\nThis capability is not part of the spec yet, and may be removed or changed at any point.\n\nRequest parameters for the logout method.\n\nTerminates the current authenticated session.",
+      "properties": {
+        "_meta": {
+          "additionalProperties": true,
+          "description": "The _meta property is reserved by ACP to allow clients and agents to attach additional\nmetadata to their interactions. Implementations MUST NOT make assumptions about values at\nthese keys.\n\nSee protocol docs: [Extensibility](https://agentclientprotocol.com/protocol/extensibility)",
+          "type": ["object", "null"]
+        }
+      },
+      "type": "object",
+      "x-method": "logout",
+      "x-side": "agent"
+    },
+    "LogoutResponse": {
+      "description": "**UNSTABLE**\n\nThis capability is not part of the spec yet, and may be removed or changed at any point.\n\nResponse to the `logout` method.",
+      "properties": {
+        "_meta": {
+          "additionalProperties": true,
+          "description": "The _meta property is reserved by ACP to allow clients and agents to attach additional\nmetadata to their interactions. Implementations MUST NOT make assumptions about values at\nthese keys.\n\nSee protocol docs: [Extensibility](https://agentclientprotocol.com/protocol/extensibility)",
+          "type": ["object", "null"]
+        }
+      },
+      "type": "object",
+      "x-method": "logout",
+      "x-side": "agent"
+    },
     "McpCapabilities": {
       "description": "MCP capabilities supported by the agent",
       "properties": {