Multi-Platform SaaS App IntegrationService Development

I am in the process of developing a robust SaaS application that needs to connect with major e-commerce and marketing platforms such as Shopify, WooCommerce, Klaviyo, Yotpo, Mailchimp, and Judge.me. I am looking for an experienced developer to build a modular IntegrationService that can effectively manage all platform connections, data synchronization via APIs and webhooks, token management, and processing of webhooks.

Key Requirements:
- The IntegrationService should handle both OAuth and API key-based integrations.
- It must be capable of normalizing data from various platforms, specifically orders, customers, reviews, and emails.
- The service should register and process webhooks with a focus on validation and retries.
- It needs to poll data periodically from platforms that do not support webhooks.
- Secure token storage and efficient refresh logic management is essential.
- The architecture should be clean, utilizing a plugin-like adapter system.

Ideal Skills and Experience:
- Proficient in .NET (C#), REST APIs, OAuth flows, and various integration patterns.
- Prior experience in building similar IntegrationServices for SaaS applications is highly desirable.
- Familiarity with AWS services such as SQS and Secrets Manager would be a significant advantage.