Q: Authenticate SharePoint user in external API I've created a SPFX feature that needs to call an external API. The external API is part of a system that has its own authentication methods outside of SharePoint. Ideally I would like to send details about the current logged in SharePoint user to this API, validate them to ensure that the user is actually logged in in SharePoint, compare the SharePoint user with the external system's user (they'll have the same email addresses) and, once matched, run the external API's code with that user.
Is there any way to go about doing something like this? If not, what is the best way to handle this sort of problem? Do other Microsoft tools like Azure need to be used for this?

A: The supported way to authenticate SharePoint framework components to a custom API is by using Azure Active Directory (AAD) and OAuth.
You need to AAD-protect your API. You can configure it so it supports two authentication mechanisms: AAD and your current authentication method. For example, if a JWT token is present, you use AAD+OAuth, and if not you use your other authentication method.
The SPFx to API authentication mechanism is described in details in the page Connect to Azure AD-secured APIs in SharePoint Framework solutions.
In summary, you will need the following elements:


*

*Register an application in Azure AD, which represents your API.

*Use a server library to protect your API with that AAD application.

*Configure your SPFx package so it has permissions to query your API.

*Grant the permissions to your SPFx package in the SharePoint central administration.

*Use the AadHttpClient in your web part to access your API.

