Slack MCP Server

Aembit supports the official Slack MCP server, which lets AI agentsAI Agent: A software workload that authenticates to systems, requests credentials, and accesses resources, either on behalf of a person or on its own. Aembit secures AI agents with the same identity-first model it uses for any workload. User-driven agents such as Claude Desktop also carry a blended identity that ties access to both the user and the agent.Learn more search and read workspace content through MCPModel Context Protocol: A standard protocol for AI agent and server interactions that defines how AI assistants communicate with external tools and data sources.Learn more(opens in new tab) tools.

This page describes how to configure Slack as an MCP serverMCP Server: A server that implements the Model Context Protocol to provide tools, resources, or data to AI agents and MCP clients.Learn more(opens in new tab) behind the Aembit MCP Identity GatewayMCP Identity Gateway: A component that brokers MCP traffic between MCP clients and target MCP servers, validating authorization and presenting Aembit-managed credentials on each request.Learn more. Each user authenticates with their own Slack identity, and the Gateway injects their token into MCP requests.

This guide builds the Gateway-to-Server PolicyGateway-to-Server Policy: The Access Policy that authorizes the MCP Identity Gateway to access an MCP server on behalf of authenticated users—the Gateway itself is the Client Workload. Also called right-side auth; each MCP server behind the Gateway needs its own.Learn more—the second of the two Access PoliciesAccess Policy: Access Policies define, enforce, and audit access between Client and Server Workloads by cryptographically verifying workload identity and contextual factors rather than relying on static secrets.Learn more the MCP Identity Gateway requires. You create the first, the Client-to-Gateway PolicyClient-to-Gateway Policy: The Access Policy that validates which MCP client can connect to the MCP Identity Gateway and authenticates users through your Identity Provider. Also called left-side auth; you create one per MCP client and Gateway combination.Learn more, during Gateway setup.

Looking for direct Slack API access?

This page covers MCP tool access through Aembit’s MCP Identity Gateway. To broker credentials for Slack’s REST API as a traditional Server WorkloadServer Workload: Server Workloads represent target services, APIs, databases, or applications that receive and respond to access requests from Client Workloads.Learn more, see the Slack Server Workload guide instead.

Prerequisites

Before you begin, ensure you have the following:

• A Slack workspace where you can create and install a Slack app
• A configured Aembit MCP Identity Gateway

Requirements and considerations

Before you configure Slack, review these requirements and behaviors specific to Slack’s MCP server.

• Restricted app types. Slack lets only internal apps and apps published in the Slack Marketplace use MCP; it rejects unlisted apps.
• No SSE transport. Slack’s MCP server supports only the Streamable HTTP transport, not Server-Sent Events (SSE).
• Use User-Based Auth. QA verified only user-based authentication for Slack; the Admin-Based (OAuth 2.0 Authorization Code) flow remains untested.

Create the app

Slack doesn’t support OAuth Dynamic Client Registration, so an administrator must register a Slack app before users can authenticate.

1. Go to Slack API: Your Apps, click Create New App, then choose From Scratch.
2. Enter an app name, select your workspace, then click Create.
3. On the App Credentials screen, copy the Client ID and Client Secret, and store them for the Credential Provider configuration.
4. Go to Agents & AI Apps and enable the Model Context Protocol toggle.
5. Go to OAuth & Permissions and opt in to PKCE. Keep this page open—you add the Aembit Callback URL and scopes after you create the Credential Provider.

Configure the Credential Provider

Create an MCP User-Based Access Token Credential ProviderCredential Provider: Credential Providers obtain the specific access credentials—such as API keys, OAuth tokens, or temporary cloud credentials—that Client Workloads need to authenticate to Server Workloads.Learn more in Aembit.

1. Log into your Aembit Tenant.

2. Go to Credential Providers in the left sidebar and click + New.

3. Configure the following fields:

   Field	Value
   Name	A user-friendly name
   Credential Type	MCP User-Based Access Token
   MCP Server URL	https://mcp.slack.com/mcp
   Client ID	The Client ID you copied earlier
   Client Secret	The Client Secret you copied earlier
   Scopes	search:read.public channels:history channels:read users:read
   PKCE Required	On

   For MCP Server URL, click Discover to populate the Authorization URL and Token URL.

4. Click Save.

5. Copy the read-only Callback URL from the Credential Provider.

Finish configuring the app

After you create the Credential Provider, copy its read-only Callback URL and return to the Slack app’s OAuth & Permissions page.

1. Under Redirect URLs, click Add New Redirect URL, paste the Aembit Callback URL, click Add, then click Save URLs.
2. Under Scopes, add the same scopes you set on the Credential Provider: search:read.public channels:history channels:read users:read
3. Install and approve the app in your Slack workspace when prompted.

Authorize the Credential Provider

1. Return to the Credential Provider in Aembit and click Authorize.

2. Complete the Slack sign-in and approve access. The Credential Provider status changes to Ready when the flow completes.

Create the Server Workload

1. Go to Server Workloads in the left sidebar and click + New.

2. Configure the following fields:

   Field	Value
   Name	A user-friendly name
   Host	mcp.slack.com
   Application Protocol	MCP
   Port	443 with TLS
   URL Path	/mcp
   Authentication method	HTTP Authentication
   Authentication scheme	Bearer

3. Click Save.

Create an Access Policy

This section creates the Gateway-to-Server Access Policy, which authorizes the MCP Identity Gateway to access Slack on behalf of authenticated users.

Create an Access Policy linking the MCP Identity Gateway (as the Client WorkloadClient Workload: Client Workloads represent software applications, scripts, or automated processes that initiate access requests to Server Workloads, operating autonomously without direct user interaction.Learn more), the Credential Provider you created, and the Server Workload for Slack.

The Gateway is the Client Workload

In this policy, the Client Workload is the MCP Identity Gateway itself—not the AI agent or individual users. The AI agent connects through the separate Client-to-Gateway policy, and the Credential Provider enforces per-user access.

For step-by-step instructions, including the Client Workload settings that identify the Gateway, see Create the gateway-to-server Access Policy.

Verify

After a user authorizes access, the Aembit AI Access Authorized page lists the Slack MCP Server as Ready. The AI agent can then call Slack MCP tools through the Gateway.