OAuth-as-a-Service for Agents: Connecting Stripe, Slack, and Notion Once

Solving the M×N integration security bottleneck with PKCE-enabled token vault gateways for autonomous agents.

The Credential Nightmare of AI Agents

Consider this typical developer flow: You are building an autonomous productivity agent. Your goal is simple: the agent needs to read customer feedback in Slack, verify their invoice details in Stripe, and draft a response document in Notion.

To achieve this, the agent must interact with three distinct APIs.

As a developer, how do you handle the credentials?

1. You go to Slack’s developer dashboard, create a custom App, configure scopes, generate a xoxb- User Token, and paste it into your server’s .env file.
2. You go to Stripe’s dashboard, generate a restricted API key, copy it, and paste it into your .env file.
3. You go to Notion’s settings, create an internal integration token, share the target pages with it, copy the token, and paste it into your .env file.

Now, your server is running with three massive, persistent, highly privileged administrative keys sitting in raw environment variables.

This works for a local sandbox. But the moment you deploy this agent to 5,000 real-world users, you hit a brick wall. You cannot ask your customers to paste their personal Stripe secret API keys into a web form. You cannot ask a corporate enterprise to supply their global Slack admin token. They will—and should—laugh you out of the room.

To make autonomous agents viable for the average consumer, we must solve the agent authentication bottleneck. We need a secure, standardized way to delegate scoped, temporary, and user-approved authority to an agent across multiple platforms. We need OAuth-as-a-Service for agents.

The M×N Authentication Bottleneck

In traditional web development, if you build an app that connects to Slack, you write an OAuth integration. You register your app with Slack, write a redirect handler, exchange the authorization code for an access token, and save it in a secure database.

Now, imagine building an AI agent platform that connects to 50 different apps (Stripe, HubSpot, Jira, Google Calendar, etc.).

If you write standard custom OAuth integrations for all 50 apps, you have an enormous engineering burden:

• You must maintain 50 distinct client credentials.
• You must handle 50 different token refresh and rotation behaviors.
• You must write custom UI authorization screens for each.

This is the M×N authentication bottleneck: M agent platforms multiplied by N target SaaS APIs. Every single agent developer is wasting months of dev cycles rebuilding the same token-exchange vault and OAuth callback endpoints.

We need a centralized, standard proxy layer. A global gateway that manages the token exchange, encryption, and rotation lifecycle, and exposes a unified, secure interface directly to your agent. This is where wmcp.sh comes in—providing a dynamic token gateway that allows an agent to authorize once and execute securely across any supported merchant or application API.

How OAuth-as-a-Service Works

The modern standard for secure agent auth relies on a Token Vault Exchange Gateway using OAuth 2.1 with PKCE (Proof Key for Code Exchange).

Instead of your agent interacting directly with the target SaaS APIs or storing master credentials, the process is delegated through a secure intermediary gateway:

[User] ──(Approves Consent)──> [OAuth Identity Provider] (e.g. Stripe, Slack)
  ▲                                       │
  │ (Auth Redirect)                       ▼ (Authorization Code)
[Agent Server] <──(Scoped Tokens)── [Token Vault Gateway] (wmcp.sh)

1. Dynamic Discovery: The agent queries the Token Vault Gateway for the target app's required scopes and authorization URL.
2. User Authorization: The agent redirects the user to the official OAuth consent screen (e.g., Stripe's Stripe Connect screen). The user approves access only for the specific, narrow scopes required.
3. Token Exchange & Vaulting: The authorization code is returned directly to the Token Vault Gateway. The gateway exchanges it for an access token and an encrypted refresh token, securing them in a hardware security module (HSM).
4. Scoped Session Token: The gateway returns a lightweight, temporary, scoped session token to your agent.
5. Secure Execution: When your agent needs to make an API call, it sends the request through the gateway using the session token. The gateway decrypts the master token, executes the API call, and returns the response. Your agent server never sees or touches the underlying master credentials.

Implementing Dynamic Token Exchange in Python

Below is a complete, production-grade Python implementation of an agent-side OAuth client. It utilizes PKCE (Proof Key for Code Exchange) to securely exchange an authorization code for an agent session token via a centralized token vault:

import base64
import hashlib
import os
import secrets
from typing import Dict, Any
import requests

class AgentOAuthClient:
    def __init__(self, gateway_url: str, app_name: str, redirect_uri: str):
        self.gateway_url = gateway_url
        self.app_name = app_name
        self.redirect_uri = redirect_uri
        self.code_verifier = ""

    def _generate_pkce_pair(self) -> Dict[str, str]:
        """Generates a secure cryptographically random verifier and high-entropy challenge."""
        # 1. Create a high-entropy verifier (minimum 43 characters)
        self.code_verifier = secrets.token_urlsafe(64)
        
        # 2. Hash using SHA-256
        sha256_hash = hashlib.sha256(self.code_verifier.encode('utf-8')).digest()
        
        # 3. Base64URL-encode the hash
        code_challenge = base64.urlsafe_b64encode(sha256_hash).decode('utf-8').replace('=', '')
        
        return {
            "code_verifier": self.code_verifier,
            "code_challenge": code_challenge
        }

    def generate_authorization_url(self, requested_scopes: list) -> str:
        """Returns the URL to redirect the user for authentication."""
        pkce = self._generate_pkce_pair()
        
        params = {
            "app": self.app_name,
            "redirect_uri": self.redirect_uri,
            "scope": " ".join(requested_scopes),
            "code_challenge": pkce["code_challenge"],
            "code_challenge_method": "S256"
        }
        
        # Build query string manually or let requests do it
        query_string = "&".join(f"{k}={requests.utils.quote(v)}" for k, v in params.items())
        return f"{self.gateway_url}/oauth/authorize?{query_string}"

    def exchange_authorization_code(self, auth_code: str) -> Dict[str, Any]:
        """Exchanges the temporary code and verifier for a secure, scoped agent token."""
        if not self.code_verifier:
            raise ValueError("No code_verifier found. You must generate an authorization URL first.")
            
        payload = {
            "app": self.app_name,
            "code": auth_code,
            "redirect_uri": self.redirect_uri,
            "code_verifier": self.code_verifier
        }
        
        response = requests.post(
            f"{self.gateway_url}/oauth/token",
            json=payload,
            headers={"Content-Type": "application/json"}
        )
        
        if response.status_code != 200:
            raise RuntimeError(f"Token exchange failed: {response.text}")
            
        # Returns the scoped agent session token (e.g., jwt_token)
        return response.json()

# Example local validation run
if __name__ == "__main__":
    # Initialize the client pointing to wmcp.sh authorization gateway
    client = AgentOAuthClient(
        gateway_url="https://wmcp.sh/api/v1",
        app_name="stripe",
        redirect_uri="https://my-agent-dashboard.com/callback"
    )
    
    # 1. Generate the URL to send the customer to
    auth_url = client.generate_authorization_url(requested_scopes=["read_charges", "read_invoices"])
    print(f"1. Redirect user to:\n{auth_url}\n")
    print(f"2. Local Code Verifier (saved in memory): {client.code_verifier[:15]}...")
    
    # Note: When the user returns to /callback with code, run:
    # session_credentials = client.exchange_authorization_code("mock_auth_code_from_callback")

Designing for Security and Compliance

When deploying agent authorization architectures, safety must be your top priority. Traditional user credentials must never be exposed to the LLM itself. By segregating authentication into a dynamic token proxy:

1. Minimal Scope: The agent is only granted the absolute minimum permissions required for the specific transaction (e.g., Stripe read_only access rather than write capabilities).
2. Complete Revocability: If the agent behaves erratically or gets caught in a loop, the user can instantly revoke the token via their SaaS dashboard, neutralizing the threat vector instantly.
3. Audit Logs: Every API request made by the agent through the token proxy is logged, stamped, and verified, providing a transparent forensic audit trail.

Stop requiring developers to build custom OAuth flows for every app they want their agent to touch. By adopting a unified, PKCE-secure agent OAuth proxy like wmcp.sh, you secure your infrastructure, protect your users, and scale your integrations in a single afternoon.