Add Airtel Money payment adapter

[sathwikshetty33]

🚀 Airtel Money Payment Adapter Integration

This PR introduces a new payment adapter for Airtel Money, enabling mobile money payments across 14 countries through the EasySwitch SDK. Addresses issue #48

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✨ What's New

• New Adapter: AirtelMoneyAdapter following the established EasySwitch adapter pattern
• Multi-country Support: Integration covers 14 African markets where Airtel Money operates
• OAuth 2.0 Authentication: Implements automatic token management and refresh
• Mobile Money Workflows: Supports USSD push and app-based payment flows

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🌍 Supported Countries & Currencies

Region	Countries & Currencies
East Africa	Uganda (UGX), Tanzania (TZS), Kenya (KES), Rwanda (RWF), Burundi (BIF)
Southern Africa	Zambia (ZMW), Malawi (MWK), Zimbabwe (ZWL), Botswana (BWP)
West Africa	Nigeria (NGN), Ghana (GHS), Senegal/Guinea-Bissau (XOF)
Central Africa	DR Congo (CDF), Ethiopia (ETB)

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🔧 Key Features

✅ Payment initialization (collection requests)
✅ Transaction status checking
✅ Webhook validation with HMAC-SHA256
✅ Refund support
✅ Transaction detail retrieval
✅ Automatic OAuth token refresh
✅ Phone number validation and formatting
✅ Multi-currency and multi-country headers

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📋 Implementation Details

🔐 Authentication

• Flow: OAuth 2.0 client credentials
• Features:
  • Automatic token caching and refresh (5 min buffer before expiry)
  • Requires: client_id, client_secret, api_key

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💸 Payment Flow

• Mobile-first: Uses phone numbers (MSISDN) as primary identifier
• Customer Experience: Push notifications to the customer's mobile device
• No web payment links: Fully USSD/App-based

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📊 Status Mapping

Airtel Status	EasySwitch Status
TS	SUCCESSFUL
TF	FAILED
TA / TP	PENDING
TR	REFUNDED
TC	CANCELLED

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🔒 Webhook Security

• HMAC-SHA256 signature validation
• Supports both x-airtel-signature and x-signature headers

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🏗️ Architecture

• Follows the same pattern as PaystackAdapter
• Inherits from BaseAdapter
• Implements all required abstract methods
• Registered via @AdaptersRegistry.register()
• Consistent error handling with PaymentError
• Returns standardized response types

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🚫 Unsupported Operations

❌ Transaction Cancellation:
Not supported by the Airtel Money API (raises UnsupportedOperationError).

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[Einswilli]

Good job!
Thanks for contributions...

Can we have a full usage example with detailed explanation for the doc under docs/assets/examples/airtel.md??? (maybe in a new PR)
And if possible add some screenshots.

[sathwikshetty33]

@Einswilli Thank You, I had a few queries, will this be merged after the docs pr and for the docs pr can you create an issue with the tag hacktoberfest attached so that is also considered for hacktoberfest.

Thank you!

[Einswilli]

@Einswilli Thank You, I had a few queries, will this be merged after the docs pr and for the docs pr can you create an issue with the tag hacktoberfest attached so that is also considered for hacktoberfest.

Thank you!

Sure @sathwikshetty33 !

[Einswilli]

Can you self assign the issue #48 please @sathwikshetty33 ???

[sathwikshetty33]

Can you self assign the issue #48 please @sathwikshetty33 ???

@Einswilli I am unable to self assign andd also it would be really helpful if you could create an issue for airtel money docs and assign that to me!

[Einswilli]

Can you self assign the issue #48 please @sathwikshetty33 ???

@Einswilli I am unable to self assign andd also it would be really helpful if you could create an issue for airtel money docs and assign that to me!

Okay, just leave a comment and i'll be able to assign it to you for the Hacktoberfest.