feat(mailgun): Add EU region support and UI configuration options

[sanyo4ever]

close https://github.com/keephq/keep/issues/5416

🎯 Overview

This PR enhances the Mailgun provider for self-hosted Keep instances with:

1. EU Region Support - Users can now use Mailgun EU accounts
2. UI Region Selection - Dropdown to choose US/EU region per provider
3. API Request Format Fix - Corrects route creation bug
4. Hybrid Configuration - Supports both UI and environment variable configuration

🐛 Problems Solved

Issue 1: EU Region Not Supported

The Mailgun API endpoint was hardcoded to https://api.mailgun.net (US region only). Users with EU Mailgun accounts received 401/400 errors when installing the provider.

Issue 2: Incorrect API Request Format

The setup_webhook() method was passing both files and data parameters to requests.post(), causing "400 Bad Request" errors from Mailgun API.

Issue 3: No UI Control for Region

Users had to modify code or use environment variables. No per-provider region configuration was possible.

✨ Solution

1. UI Dropdown for Region Selection

Added api_region field to MailgunProviderAuthConfig with dropdown:

• Type: Select field with options ["US", "EU"]
• Optional: Can be left empty to use environment variable
• User-friendly: Clear hints and descriptions

2. Hybrid Configuration Priority

region = (
    self.authentication_config.api_region  # 1. Check UI field first
    or MailgunProvider.MAILGUN_REGION      # 2. Fall back to env var
    or "US"                                 # 3. Default to US
).upper()

Benefits:

• Per-provider region configuration (UI)
• Global default via MAILGUN_REGION environment variable
• Backward compatible (existing deployments unaffected)
• Flexible for multi-region deployments

3. API Endpoint Selection

Dynamically selects the correct API endpoint:

• US Region: https://api.mailgun.net
• EU Region: https://api.eu.mailgun.net

4. API Request Format Fix

Before (Broken):

response = requests.post(
    url,
    files=payload,  # ❌ Wrong parameter
    auth=("api", key),
    data=payload,   # ❌ Missing action array
)

After (Fixed):

response = requests.post(
    url,
    auth=("api", key),
    data={
        **payload,
        "action": [  # ✅ Correct format
            f"forward('{keep_api_url}&api_key={api_key}')",
            "stop()",
        ],
    },
)

🧪 Testing

• ✅ Tested with US region Mailgun account
• ✅ Tested with EU region Mailgun account
• ✅ Route creation works correctly in both regions
• ✅ UI dropdown displays and saves correctly
• ✅ Environment variable fallback works
• ✅ Backward compatible (defaults to US)
• ✅ No linting errors

📊 Changes

Files Modified:

• keep/providers/mailgun_provider/mailgun_provider.py
  • Added api_region field with dropdown (lines 49-59)
  • Added MAILGUN_REGION class variable (line 74)
  • Dynamic API endpoint selection (lines 222-229)
  • Fixed request format in setup_webhook() (lines 231-259)

🔄 Backward Compatibility

• ✅ Existing deployments unaffected (defaults to US region)
• ✅ Environment variable MAILGUN_REGION still works
• ✅ No breaking changes to configuration
• ✅ Works with both old and new Mailgun API key formats

💡 Usage Examples

Example 1: UI Configuration (Per-Provider)