feat: add mcpOAuthTokenStorage support across all SDKs

Add the mcpOAuthTokenStorage protocol property to session creation and
resume flows in all five language SDKs (Node.js, Python, Go, .NET, Rust).

When set to "in-memory", the runtime uses an in-memory MCP OAuth token
store instead of the OS keychain. The SDK defaults to "in-memory" for
safe multitenant behavior.

- Node.js: Add to SessionConfig interface and ResumeSessionConfig Pick type
- Python: Add to both TypedDicts and client methods with docstrings
- Go: Add to config structs, wire request structs, and client wiring
- .NET: Add McpOAuthTokenStorageMode enum with JsonStringEnumConverter,
  update config classes, copy constructors, wire records, and serialization
  context
- Rust: Add field, builder methods, Default/new impls, and Debug impls

Tests:
- Rust: Assert defaults and builder composition in existing type tests
- .NET: Add property to SessionConfig_Clone_CopiesAllProperties test
- Go: Add wire serialization tests for both request types

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: MackinnonBuck

dotnet/src/Client.cs

@@ -616,6 +616,7 @@ public async Task<CopilotSession> CreateSessionAsync(SessionConfig config, Cance
                 config.Streaming is true ? true : null,
                 config.IncludeSubAgentStreamingEvents,
                 config.McpServers,
+                config.McpOAuthTokenStorage ?? McpOAuthTokenStorageMode.InMemory,
                 "direct",
                 config.CustomAgents,
                 config.DefaultAgent,
@@ -780,6 +781,7 @@ public async Task<CopilotSession> ResumeSessionAsync(string sessionId, ResumeSes
                 config.Streaming is true ? true : null,
                 config.IncludeSubAgentStreamingEvents,
                 config.McpServers,
+                config.McpOAuthTokenStorage ?? McpOAuthTokenStorageMode.InMemory,
                 "direct",
                 config.CustomAgents,
                 config.DefaultAgent,
@@ -1986,6 +1988,7 @@ internal record CreateSessionRequest(
         bool? Streaming,
         bool? IncludeSubAgentStreamingEvents,
         IDictionary<string, McpServerConfig>? McpServers,
+        McpOAuthTokenStorageMode? McpOAuthTokenStorage,
         string? EnvValueMode,
         IList<CustomAgentConfig>? CustomAgents,
         DefaultAgentConfig? DefaultAgent,
@@ -2050,6 +2053,7 @@ internal record ResumeSessionRequest(
         bool? Streaming,
         bool? IncludeSubAgentStreamingEvents,
         IDictionary<string, McpServerConfig>? McpServers,
+        McpOAuthTokenStorageMode? McpOAuthTokenStorage,
         string? EnvValueMode,
         IList<CustomAgentConfig>? CustomAgents,
         DefaultAgentConfig? DefaultAgent,
@@ -2139,6 +2143,7 @@ internal record PermissionRequestResponseV2(
     [JsonSerializable(typeof(ListSessionsResponse))]
     [JsonSerializable(typeof(GetSessionMetadataRequest))]
     [JsonSerializable(typeof(GetSessionMetadataResponse))]
+    [JsonSerializable(typeof(McpOAuthTokenStorageMode))]
     [JsonSerializable(typeof(ModelCapabilitiesOverride))]
     [JsonSerializable(typeof(PermissionRequestResult))]
     [JsonSerializable(typeof(PermissionRequestResultKind))]

dotnet/src/Types.cs

@@ -1804,6 +1804,21 @@ public enum McpHttpServerConfigOauthGrantType
     ClientCredentials
 }
 
+/// <summary>
+/// Controls how MCP OAuth tokens are stored for a session.
+/// </summary>
+[JsonConverter(typeof(JsonStringEnumConverter<McpOAuthTokenStorageMode>))]
+public enum McpOAuthTokenStorageMode
+{
+    /// <summary>Tokens are stored in the OS keychain, shared across sessions.</summary>
+    [JsonStringEnumMemberName("persistent")]
+    Persistent,
+
+    /// <summary>Tokens are stored in memory and discarded when the session ends.</summary>
+    [JsonStringEnumMemberName("in-memory")]
+    InMemory
+}
+
 /// <summary>
 /// Abstract base class for MCP server configurations.
 /// </summary>
@@ -2085,6 +2100,7 @@ protected SessionConfig(SessionConfig? other)
                 ? new Dictionary<string, McpServerConfig>(dict, dict.Comparer)
                 : new Dictionary<string, McpServerConfig>(other.McpServers))
             : null;
+        McpOAuthTokenStorage = other.McpOAuthTokenStorage;
         Model = other.Model;
         ModelCapabilities = other.ModelCapabilities;
         OnAutoModeSwitch = other.OnAutoModeSwitch;
@@ -2261,6 +2277,12 @@ protected SessionConfig(SessionConfig? other)
     /// </summary>
     public IDictionary<string, McpServerConfig>? McpServers { get; set; }
 
+    /// <summary>
+    /// Controls how MCP OAuth tokens are stored for this session.
+    /// Default: <see cref="McpOAuthTokenStorageMode.InMemory"/> for safe multitenant behavior.
+    /// </summary>
+    public McpOAuthTokenStorageMode? McpOAuthTokenStorage { get; set; }
+
     /// <summary>
     /// Custom agent configurations for the session.
     /// </summary>
@@ -2394,6 +2416,7 @@ protected ResumeSessionConfig(ResumeSessionConfig? other)
                 ? new Dictionary<string, McpServerConfig>(dict, dict.Comparer)
                 : new Dictionary<string, McpServerConfig>(other.McpServers))
             : null;
+        McpOAuthTokenStorage = other.McpOAuthTokenStorage;
         Model = other.Model;
         ModelCapabilities = other.ModelCapabilities;
         OnAutoModeSwitch = other.OnAutoModeSwitch;
@@ -2587,6 +2610,12 @@ protected ResumeSessionConfig(ResumeSessionConfig? other)
     /// </summary>
     public IDictionary<string, McpServerConfig>? McpServers { get; set; }
 
+    /// <summary>
+    /// Controls how MCP OAuth tokens are stored for this session.
+    /// Default: <see cref="McpOAuthTokenStorageMode.InMemory"/> for safe multitenant behavior.
+    /// </summary>
+    public McpOAuthTokenStorageMode? McpOAuthTokenStorage { get; set; }
+
     /// <summary>
     /// Custom agent configurations for the session.
     /// </summary>

dotnet/test/Unit/CloneTests.cs

@@ -94,6 +94,7 @@ public void SessionConfig_Clone_CopiesAllProperties()
             EnableSessionTelemetry = false,
             IncludeSubAgentStreamingEvents = false,
             McpServers = new Dictionary<string, McpServerConfig> { ["server1"] = new McpStdioServerConfig { Command = "echo" } },
+            McpOAuthTokenStorage = McpOAuthTokenStorageMode.Persistent,
             CustomAgents = [new CustomAgentConfig { Name = "agent1", Model = "claude-haiku-4.5" }],
             Agent = "agent1",
             Cloud = new CloudSessionOptions
@@ -127,6 +128,7 @@ public void SessionConfig_Clone_CopiesAllProperties()
         Assert.Equal(original.EnableSessionTelemetry, clone.EnableSessionTelemetry);
         Assert.Equal(original.IncludeSubAgentStreamingEvents, clone.IncludeSubAgentStreamingEvents);
         Assert.Equal(original.McpServers.Count, clone.McpServers!.Count);
+        Assert.Equal(original.McpOAuthTokenStorage, clone.McpOAuthTokenStorage);
         Assert.Equal(original.CustomAgents.Count, clone.CustomAgents!.Count);
         Assert.Equal(original.CustomAgents[0].Model, clone.CustomAgents[0].Model);
         Assert.Equal(original.Agent, clone.Agent);

go/client.go

@@ -636,6 +636,11 @@ func (c *Client) CreateSession(ctx context.Context, config *SessionConfig) (*Ses
 	req.ModelCapabilities = config.ModelCapabilities
 	req.WorkingDirectory = config.WorkingDirectory
 	req.MCPServers = config.MCPServers
+	if config.McpOAuthTokenStorage != "" {
+		req.McpOAuthTokenStorage = config.McpOAuthTokenStorage
+	} else {
+		req.McpOAuthTokenStorage = "in-memory"
+	}
 	req.EnvValueMode = "direct"
 	req.CustomAgents = config.CustomAgents
 	req.DefaultAgent = config.DefaultAgent
@@ -841,6 +846,11 @@ func (c *Client) ResumeSessionWithOptions(ctx context.Context, sessionID string,
 		req.ContinuePendingWork = Bool(true)
 	}
 	req.MCPServers = config.MCPServers
+	if config.McpOAuthTokenStorage != "" {
+		req.McpOAuthTokenStorage = config.McpOAuthTokenStorage
+	} else {
+		req.McpOAuthTokenStorage = "in-memory"
+	}
 	req.EnvValueMode = "direct"
 	req.CustomAgents = config.CustomAgents
 	req.DefaultAgent = config.DefaultAgent

go/client_test.go

@@ -615,6 +615,60 @@ func TestResumeSessionRequest_InstructionDirectories(t *testing.T) {
 	})
 }
 
+func TestCreateSessionRequest_McpOAuthTokenStorage(t *testing.T) {
+	t.Run("includes mcpOAuthTokenStorage in JSON when set", func(t *testing.T) {
+		req := createSessionRequest{McpOAuthTokenStorage: "in-memory"}
+		data, err := json.Marshal(req)
+		if err != nil {
+			t.Fatalf("Failed to marshal: %v", err)
+		}
+		var m map[string]any
+		if err := json.Unmarshal(data, &m); err != nil {
+			t.Fatalf("Failed to unmarshal: %v", err)
+		}
+		if m["mcpOAuthTokenStorage"] != "in-memory" {
+			t.Errorf("Expected mcpOAuthTokenStorage to be 'in-memory', got %v", m["mcpOAuthTokenStorage"])
+		}
+	})
+
+	t.Run("omits mcpOAuthTokenStorage from JSON when empty", func(t *testing.T) {
+		req := createSessionRequest{}
+		data, _ := json.Marshal(req)
+		var m map[string]any
+		json.Unmarshal(data, &m)
+		if _, ok := m["mcpOAuthTokenStorage"]; ok {
+			t.Error("Expected mcpOAuthTokenStorage to be omitted when empty")
+		}
+	})
+}
+
+func TestResumeSessionRequest_McpOAuthTokenStorage(t *testing.T) {
+	t.Run("includes mcpOAuthTokenStorage in JSON when set", func(t *testing.T) {
+		req := resumeSessionRequest{SessionID: "s1", McpOAuthTokenStorage: "persistent"}
+		data, err := json.Marshal(req)
+		if err != nil {
+			t.Fatalf("Failed to marshal: %v", err)
+		}
+		var m map[string]any
+		if err := json.Unmarshal(data, &m); err != nil {
+			t.Fatalf("Failed to unmarshal: %v", err)
+		}
+		if m["mcpOAuthTokenStorage"] != "persistent" {
+			t.Errorf("Expected mcpOAuthTokenStorage to be 'persistent', got %v", m["mcpOAuthTokenStorage"])
+		}
+	})
+
+	t.Run("omits mcpOAuthTokenStorage from JSON when empty", func(t *testing.T) {
+		req := resumeSessionRequest{SessionID: "s1"}
+		data, _ := json.Marshal(req)
+		var m map[string]any
+		json.Unmarshal(data, &m)
+		if _, ok := m["mcpOAuthTokenStorage"]; ok {
+			t.Error("Expected mcpOAuthTokenStorage to be omitted when empty")
+		}
+	})
+}
+
 func TestOverridesBuiltInTool(t *testing.T) {
 	t.Run("OverridesBuiltInTool is serialized in tool definition", func(t *testing.T) {
 		tool := Tool{

go/types.go

@@ -658,6 +658,11 @@ type SessionConfig struct {
 	ModelCapabilities *rpc.ModelCapabilitiesOverride
 	// MCPServers configures MCP servers for the session
 	MCPServers map[string]MCPServerConfig
+	// McpOAuthTokenStorage controls how MCP OAuth tokens are stored for this session.
+	// "persistent" stores tokens in the OS keychain (shared across sessions).
+	// "in-memory" stores tokens in memory and discards them when the session ends.
+	// Defaults to "in-memory" for safe multitenant behavior.
+	McpOAuthTokenStorage string
 	// CustomAgents configures custom agents for the session
 	CustomAgents []CustomAgentConfig
 	// DefaultAgent configures the default agent (the built-in agent that handles turns when no custom agent is selected).
@@ -902,6 +907,11 @@ type ResumeSessionConfig struct {
 	IncludeSubAgentStreamingEvents *bool
 	// MCPServers configures MCP servers for the session
 	MCPServers map[string]MCPServerConfig
+	// McpOAuthTokenStorage controls how MCP OAuth tokens are stored for this session.
+	// "persistent" stores tokens in the OS keychain (shared across sessions).
+	// "in-memory" stores tokens in memory and discards them when the session ends.
+	// Defaults to "in-memory" for safe multitenant behavior.
+	McpOAuthTokenStorage string
 	// CustomAgents configures custom agents for the session
 	CustomAgents []CustomAgentConfig
 	// DefaultAgent configures the default agent (the built-in agent that handles turns when no custom agent is selected).
@@ -1162,6 +1172,7 @@ type createSessionRequest struct {
 	Streaming                      *bool                          `json:"streaming,omitempty"`
 	IncludeSubAgentStreamingEvents *bool                          `json:"includeSubAgentStreamingEvents,omitempty"`
 	MCPServers                     map[string]MCPServerConfig     `json:"mcpServers,omitempty"`
+	McpOAuthTokenStorage           string                         `json:"mcpOAuthTokenStorage,omitempty"`
 	EnvValueMode                   string                         `json:"envValueMode,omitempty"`
 	CustomAgents                   []CustomAgentConfig            `json:"customAgents,omitempty"`
 	DefaultAgent                   *DefaultAgentConfig            `json:"defaultAgent,omitempty"`
@@ -1220,6 +1231,7 @@ type resumeSessionRequest struct {
 	Streaming                      *bool                          `json:"streaming,omitempty"`
 	IncludeSubAgentStreamingEvents *bool                          `json:"includeSubAgentStreamingEvents,omitempty"`
 	MCPServers                     map[string]MCPServerConfig     `json:"mcpServers,omitempty"`
+	McpOAuthTokenStorage           string                         `json:"mcpOAuthTokenStorage,omitempty"`
 	EnvValueMode                   string                         `json:"envValueMode,omitempty"`
 	CustomAgents                   []CustomAgentConfig            `json:"customAgents,omitempty"`
 	DefaultAgent                   *DefaultAgentConfig            `json:"defaultAgent,omitempty"`

nodejs/src/client.ts

@@ -824,6 +824,7 @@ export class CopilotClient {
                 streaming: config.streaming,
                 includeSubAgentStreamingEvents: config.includeSubAgentStreamingEvents ?? true,
                 mcpServers: config.mcpServers,
+                mcpOAuthTokenStorage: config.mcpOAuthTokenStorage ?? "in-memory",
                 envValueMode: "direct",
                 customAgents: config.customAgents,
                 defaultAgent: config.defaultAgent,
@@ -981,6 +982,7 @@ export class CopilotClient {
                 streaming: config.streaming,
                 includeSubAgentStreamingEvents: config.includeSubAgentStreamingEvents ?? true,
                 mcpServers: config.mcpServers,
+                mcpOAuthTokenStorage: config.mcpOAuthTokenStorage ?? "in-memory",
                 envValueMode: "direct",
                 customAgents: config.customAgents,
                 defaultAgent: config.defaultAgent,

nodejs/src/types.ts

@@ -1444,6 +1444,15 @@ export interface SessionConfig {
      */
     includeSubAgentStreamingEvents?: boolean;
 
+    /**
+     * Controls how MCP OAuth tokens are stored for this session.
+     * - `"persistent"` — tokens are stored in the OS keychain (shared across sessions)
+     * - `"in-memory"` — tokens are stored in memory and discarded when the session ends
+     *
+     * @default "in-memory"
+     */
+    mcpOAuthTokenStorage?: "persistent" | "in-memory";
+
     /**
      * MCP server configurations for the session.
      * Keys are server names, values are server configurations.
@@ -1567,6 +1576,7 @@ export type ResumeSessionConfig = Pick<
     | "customAgents"
     | "defaultAgent"
     | "agent"
+    | "mcpOAuthTokenStorage"
     | "skillDirectories"
     | "instructionDirectories"
     | "disabledSkills"

python/copilot/client.py

@@ -1340,6 +1340,7 @@ async def create_session(
         streaming: bool | None = None,
         include_sub_agent_streaming_events: bool | None = None,
         mcp_servers: dict[str, MCPServerConfig] | None = None,
+        mcp_oauth_token_storage: Literal["persistent", "in-memory"] | None = None,
         custom_agents: list[CustomAgentConfig] | None = None,
         default_agent: DefaultAgentConfig | dict[str, Any] | None = None,
         agent: str | None = None,
@@ -1402,6 +1403,10 @@ async def create_session(
                 ``agentId`` set). When False, only non-streaming sub-agent events and
                 ``subagent.*`` lifecycle events are forwarded. Defaults to True.
             mcp_servers: MCP server configurations.
+            mcp_oauth_token_storage: Controls how MCP OAuth tokens are stored.
+                ``"persistent"`` uses the OS keychain (shared across sessions).
+                ``"in-memory"`` stores tokens in memory (discarded on session end).
+                Defaults to ``"in-memory"`` for safe multitenant behavior.
             custom_agents: Custom agent configurations.
             default_agent: Configuration for the default agent,
                 including tool visibility controls.
@@ -1551,6 +1556,8 @@ async def create_session(
         # Add MCP servers configuration if provided
         if mcp_servers:
             payload["mcpServers"] = mcp_servers
+        # Default MCP OAuth token storage to in-memory for safe multitenant behavior
+        payload["mcpOAuthTokenStorage"] = mcp_oauth_token_storage or "in-memory"
         payload["envValueMode"] = "direct"
 
         # Add custom agents configuration if provided
@@ -1713,6 +1720,7 @@ async def resume_session(
         streaming: bool | None = None,
         include_sub_agent_streaming_events: bool | None = None,
         mcp_servers: dict[str, MCPServerConfig] | None = None,
+        mcp_oauth_token_storage: Literal["persistent", "in-memory"] | None = None,
         custom_agents: list[CustomAgentConfig] | None = None,
         default_agent: DefaultAgentConfig | dict[str, Any] | None = None,
         agent: str | None = None,
@@ -1775,6 +1783,10 @@ async def resume_session(
                 ``agentId`` set). When False, only non-streaming sub-agent events and
                 ``subagent.*`` lifecycle events are forwarded. Defaults to True.
             mcp_servers: MCP server configurations.
+            mcp_oauth_token_storage: Controls how MCP OAuth tokens are stored.
+                ``"persistent"`` uses the OS keychain (shared across sessions).
+                ``"in-memory"`` stores tokens in memory (discarded on session end).
+                Defaults to ``"in-memory"`` for safe multitenant behavior.
             custom_agents: Custom agent configurations.
             default_agent: Configuration for the default agent,
                 including tool visibility controls.
@@ -1918,6 +1930,8 @@ async def resume_session(
         # TODO: disable_resume is not a keyword arg yet; keeping for future use
         if mcp_servers:
             payload["mcpServers"] = mcp_servers
+        # Default MCP OAuth token storage to in-memory for safe multitenant behavior
+        payload["mcpOAuthTokenStorage"] = mcp_oauth_token_storage or "in-memory"
         payload["envValueMode"] = "direct"
 
         if custom_agents:

python/copilot/session.py

@@ -947,6 +947,11 @@ class SessionConfig(TypedDict, total=False):
     include_sub_agent_streaming_events: bool
     # MCP server configurations for the session
     mcp_servers: dict[str, MCPServerConfig]
+    # Controls how MCP OAuth tokens are stored for this session.
+    # "persistent" stores tokens in the OS keychain (shared across sessions).
+    # "in-memory" stores tokens in memory, discarded when the session ends.
+    # Defaults to "in-memory" for safe multitenant behavior.
+    mcp_oauth_token_storage: Literal["persistent", "in-memory"]
     # Custom agent configurations for the session
     custom_agents: list[CustomAgentConfig]
     # Configuration for the default agent.
@@ -1034,6 +1039,11 @@ class ResumeSessionConfig(TypedDict, total=False):
     include_sub_agent_streaming_events: bool
     # MCP server configurations for the session
     mcp_servers: dict[str, MCPServerConfig]
+    # Controls how MCP OAuth tokens are stored for this session.
+    # "persistent" stores tokens in the OS keychain (shared across sessions).
+    # "in-memory" stores tokens in memory, discarded when the session ends.
+    # Defaults to "in-memory" for safe multitenant behavior.
+    mcp_oauth_token_storage: Literal["persistent", "in-memory"]
     # Custom agent configurations for the session
     custom_agents: list[CustomAgentConfig]
     # Configuration for the default agent.