Approval Webhooks

Overview

When a workflow reaches a human_approval step, Station can notify external systems via webhooks. This enables human-in-the-loop automation with:

Slack notifications with approve/reject buttons
ntfy.sh alerts for mobile push notifications
PagerDuty escalations for critical decisions
Custom dashboards showing pending approvals

┌─────────────────────────────────────────────────────────────────────────────┐
│                        APPROVAL WEBHOOK FLOW                                 │
└─────────────────────────────────────────────────────────────────────────────┘

     ┌──────────────┐
     │   Workflow   │
     │   Running    │
     └──────┬───────┘
            │
            ▼
┌───────────────────────┐
│   human_approval      │
│       step            │
└───────────┬───────────┘
            │
            ▼
┌───────────────────────┐     ┌─────────────────────────────────────┐
│  Create Approval      │     │         WEBHOOK NOTIFICATION        │
│  Record in DB         │     │                                     │
└───────────┬───────────┘     │  POST https://ntfy.sh/your-topic    │
            │                 │                                     │
            ├────────────────▶│  {                                  │
            │                 │    "event": "approval.requested",   │
            │                 │    "approval_id": "appr-abc123",    │
            │                 │    "message": "Approve deploy?",    │
            │                 │    "approve_url": "http://...",     │
            │                 │    "reject_url": "http://..."       │
            │                 │  }                                  │
            │                 └─────────────────────────────────────┘
            │
            ▼
┌───────────────────────┐
│   WORKFLOW PAUSED     │◄───────────────────────────────┐
│   (waiting_approval)  │                                │
└───────────┬───────────┘                                │
            │                                            │
            │         Human reviews notification         │
            │                                            │
            ▼                                            │
     ┌──────────────┐                                    │
     │   Decision   │                                    │
     └──────┬───────┘                                    │
            │                                            │
    ┌───────┴───────┐                                    │
    │               │                                    │
    ▼               ▼                                    │
┌────────┐    ┌──────────┐                              │
│APPROVE │    │  REJECT  │                              │
└───┬────┘    └────┬─────┘                              │
    │              │       API Call                     │
    │              ├───────────────────────────────────►│
    │              │  POST /workflow-approvals/{id}/reject
    │    API Call  │                                    │
    ├──────────────┼───────────────────────────────────►│
    │              │  POST /workflow-approvals/{id}/approve
    ▼              ▼
┌────────────────────────┐
│   Workflow Continues   │
│   or Fails             │
└────────────────────────┘

Configuration

Config File

Add to your config.yaml:

notifications:
  # Webhook URL to POST when approval is requested
  approval_webhook_url: "https://ntfy.sh/station-approvals"
  
  # Timeout for webhook delivery (default: 10 seconds)
  approval_webhook_timeout: 10

Environment Variables

export STN_APPROVAL_WEBHOOK_URL="https://ntfy.sh/station-approvals"
export STN_APPROVAL_WEBHOOK_TIMEOUT=10

Webhook Payload

When a workflow reaches a human_approval step, Station sends:

{
  "event": "approval.requested",
  "approval_id": "appr-run123-approve_deploy",
  "workflow_id": "deploy-production",
  "workflow_name": "Production Deployment",
  "run_id": "run-abc123",
  "step_name": "approve_deploy",
  "message": "Approve deployment of api-service v2.3.0 to production?",
  "approvers": ["oncall-sre", "platform-leads"],
  "timeout_seconds": 1800,
  "created_at": "2025-01-04T17:30:00Z",
  "approve_url": "http://localhost:8587/workflow-approvals/appr-run123-approve_deploy/approve",
  "reject_url": "http://localhost:8587/workflow-approvals/appr-run123-approve_deploy/reject"
}

Payload Fields

Field	Type	Description
`event`	string	Always `"approval.requested"`
`approval_id`	string	Unique ID for this approval request
`workflow_id`	string	ID of the workflow definition
`workflow_name`	string	Human-readable workflow name
`run_id`	string	ID of this workflow run instance
`step_name`	string	Name of the approval step
`message`	string	Human-readable message (supports template variables)
`approvers`	array	List of allowed approvers (optional)
`timeout_seconds`	int	Seconds until approval expires
`created_at`	string	ISO 8601 timestamp
`approve_url`	string	URL to POST for approval
`reject_url`	string	URL to POST for rejection

Integration Examples

ntfy.sh

ntfy is a simple HTTP-based pub-sub notification service - perfect for mobile push notifications.

Install the ntfy app

Get it on Android or iOS

Subscribe to your topic

Open the app and subscribe to station-approvals (or your chosen topic name)

Configure Station

notifications:
  approval_webhook_url: https://ntfy.sh/station-approvals
  approval_webhook_timeout: 10

Test the webhook

curl -d "Test notification from Station" https://ntfy.sh/station-approvals

For rich notifications with titles, priorities, and action buttons, use a webhook proxy that transforms Station’s JSON payload into ntfy’s format. See the advanced examples below.

Slack

Configure a Slack Incoming Webhook:

notifications:
  approval_webhook_url: "https://hooks.slack.com/services/T00000000/B00000000/XXXXXXXX"

For interactive approve/reject buttons, you’ll need a small webhook proxy to transform the payload into Slack Block Kit format:

{
  "blocks": [
    {
      "type": "section",
      "text": {
        "type": "mrkdwn",
        "text": "*Approval Required*\n\nApprove deployment of `api-service v2.3.0` to production?"
      }
    },
    {
      "type": "actions",
      "elements": [
        {
          "type": "button",
          "text": { "type": "plain_text", "text": "Approve" },
          "style": "primary",
          "url": "http://station:8587/workflow-approvals/appr-abc123/approve"
        },
        {
          "type": "button",
          "text": { "type": "plain_text", "text": "Reject" },
          "style": "danger",
          "url": "http://station:8587/workflow-approvals/appr-abc123/reject"
        }
      ]
    }
  ]
}

PagerDuty

Send approval requests as PagerDuty incidents:

notifications:
  approval_webhook_url: "https://events.pagerduty.com/v2/enqueue"

You’ll need a webhook proxy to transform to PagerDuty Events API v2 format.

Custom Webhook Proxy

Build a simple proxy to transform Station’s payload for any system:

from flask import Flask, request
import requests

app = Flask(__name__)

NTFY_TOPIC = "https://ntfy.sh/station-approvals"

@app.route('/webhook', methods=['POST'])
def handle_approval():
    data = request.json
    
    # Build ntfy message with actions
    message = f"{data['message']}\n\nWorkflow: {data['workflow_name']}"
    
    headers = {
        "Title": "Approval Required",
        "Priority": "high",
        "Tags": "warning",
        "Actions": f"http, Approve, {data['approve_url']}; http, Reject, {data['reject_url']}"
    }
    
    requests.post(NTFY_TOPIC, data=message, headers=headers)
    return {"status": "ok"}

if __name__ == '__main__':
    app.run(port=5000)

Then configure Station to use your proxy:

notifications:
  approval_webhook_url: http://localhost:5000/webhook

Approval API

Once notified, approvers can use the URLs in the payload or call the API directly.

Approve a Request

curl -X POST http://localhost:8587/workflow-approvals/{approval_id}/approve \
  -H "Content-Type: application/json" \
  -d '{"comment": "Reviewed and approved"}'

Response:

{
  "approval_id": "appr-abc123",
  "status": "approved",
  "decided_by": "api-user",
  "decided_at": "2025-01-04T17:35:00Z"
}

Reject a Request

curl -X POST http://localhost:8587/workflow-approvals/{approval_id}/reject \
  -H "Content-Type: application/json" \
  -d '{"reason": "Missing security review"}'

CLI Commands

# List pending approvals
stn workflow approvals list --status pending

# Approve
stn workflow approvals approve appr-abc123 --comment "LGTM"

# Reject  
stn workflow approvals reject appr-abc123 --reason "Needs review"

# Get details
stn workflow approvals get appr-abc123

Audit Logging

All webhook deliveries and approval decisions are logged for compliance and debugging.

Webhook Delivery Logs

Every webhook attempt is recorded with:

Request payload sent
Response status code
Response body (truncated)
Duration in milliseconds
Error message (if failed)

View Audit Trail

curl http://localhost:8587/workflow-approvals/{approval_id}/audit

Response:

{
  "logs": [
    {
      "event_type": "webhook.attempt",
      "webhook_url": "https://ntfy.sh/station-approvals",
      "created_at": "2025-01-04T17:30:00.100Z"
    },
    {
      "event_type": "webhook.success",
      "response_status": 200,
      "duration_ms": 150,
      "created_at": "2025-01-04T17:30:00.250Z"
    },
    {
      "event_type": "approval.approved",
      "metadata": {
        "decided_by": "alice@example.com",
        "comment": "Looks good"
      },
      "created_at": "2025-01-04T17:35:00Z"
    }
  ]
}

Audit Event Types

Event Type	Description
`webhook.attempt`	Webhook delivery started
`webhook.success`	Webhook delivered successfully (2xx)
`webhook.failure`	Webhook delivery failed
`approval.approved`	Approval was granted
`approval.rejected`	Approval was denied
`approval.timeout`	Approval expired without decision

Retry Behavior

Station automatically retries failed webhook deliveries:

Max retries: 3 attempts
Backoff: Exponential (1s, 4s, 9s)
Timeout: Configurable per-request (default 10s)

All retry attempts are logged in the audit trail.

Troubleshooting

Webhook not received

Verify webhook URL is correct:

curl -X POST "YOUR_WEBHOOK_URL" \
  -H "Content-Type: application/json" \
  -d '{"test": true}'

Check Station logs:

STN_LOG_LEVEL=debug stn serve 2>&1 | grep -i webhook

Check audit logs:

curl http://localhost:8587/workflow-approvals/{id}/audit

Webhook returns non-2xx

Check the audit log for the response body:

SELECT event_type, response_status, error_message 
FROM notification_logs 
WHERE approval_id = 'appr-xxx'
ORDER BY created_at DESC;

Approval URL not working

Verify Station is accessible from where approvals happen
Check approval hasn’t expired: stn workflow approvals get appr-xxx
Check approval wasn’t already decided

Workflow stuck after approval

Check workflow run status: stn workflow runs get run-xyz --steps
Check NATS is running: stn status
Check logs for errors

Security Considerations

Always use HTTPS for webhook URLs in production to protect approval payloads.

Recommendations

Use HTTPS - Encrypt webhook traffic
Protect approval API - Run Station on internal network or use authentication
Audit retention - Configure log retention for compliance
Validate approvers - Use the approvers field to restrict who can approve

Comparison: Notifications vs Approval Webhooks

Feature	Notify Tool	Approval Webhooks
Trigger	Agent calls `notify()`	Workflow hits `human_approval` step
Purpose	Alert users about events	Block workflow until human decision
Payload	Customizable message	Structured approval request
Response	Fire-and-forget	Approve/reject via API
Config	`notify:` section	`notifications:` section

Next Steps

Workflows - Create workflows with approval steps
Notifications - Agent-initiated notifications
Webhooks - Trigger agents from external systems

Get Started

Station CLI

Building Agents

Station Lattice

Deployment

Advanced

Overview

Configuration

Config File

Environment Variables

Webhook Payload

Payload Fields

Integration Examples

ntfy.sh

Slack

PagerDuty

Custom Webhook Proxy

Approval API

Approve a Request

Reject a Request

CLI Commands

Audit Logging

Webhook Delivery Logs

View Audit Trail

Audit Event Types

Retry Behavior

Troubleshooting

Security Considerations

Recommendations

Comparison: Notifications vs Approval Webhooks

Next Steps

Get Started

Station CLI

Building Agents

Station Lattice

Deployment

Advanced

​Overview

​Configuration

​Config File

​Environment Variables

​Webhook Payload

​Payload Fields

​Integration Examples

​ntfy.sh

​Slack

​PagerDuty

​Custom Webhook Proxy

​Approval API

​Approve a Request

​Reject a Request

​CLI Commands

​Audit Logging

​Webhook Delivery Logs

​View Audit Trail

​Audit Event Types

​Retry Behavior

​Troubleshooting

​Security Considerations

​Recommendations

​Comparison: Notifications vs Approval Webhooks

​Next Steps

Overview

Configuration

Config File

Environment Variables

Webhook Payload

Payload Fields

Integration Examples

ntfy.sh

Slack

PagerDuty

Custom Webhook Proxy

Approval API

Approve a Request

Reject a Request

CLI Commands

Audit Logging

Webhook Delivery Logs

View Audit Trail

Audit Event Types

Retry Behavior

Troubleshooting

Security Considerations

Recommendations

Comparison: Notifications vs Approval Webhooks

Next Steps