How to Get Your Microsoft Advertising API Key

Microsoft Advertising requires a combination of a Developer Token, OAuth 2.0 credentials from a Microsoft Entra ID app registration, and user authorization flow to access its API, as there is no single API key for access. In 2026, developers must choose between the soon-to-be-deprecated SOAP API and the newer REST API, with the latter being recommended for new integrations due to the SOAP API's feature freeze starting October 1, 2026, and complete decommissioning by January 31, 2027. The process involves creating an app registration in Microsoft Entra ID, requesting a Developer Token, and implementing OAuth user authorization, with Microsoft Advertising's REST API requiring specific headers for authenticated calls. Notably, Microsoft Advertising does not support service-principal OAuth flows, instead relying on delegated user OAuth, and offers a separate sandbox environment for testing. The document also highlights the importance of credential management, such as storing sensitive information securely and refreshing tokens proactively, while comparing Microsoft Advertising's approach with other platforms like Google Ads and discussing the potential benefits of using a unified API solution for managing multiple advertising integrations.