Use single sign-on (SSO) or cross-origin resource sharing (CORS) in your event-based or spam-reporting Outlook add-in
When an Outlook add-in implements event-based activation or integrated spam reporting, the events run in a separate runtime. To configure single sign-on (SSO) or request external data through cross-origin resource sharing (CORS) in these add-ins, you must configure a well-known URI. Through this resource, Office will be able to identify the add-ins, including their JavaScript files, that support SSO or CORS requests.
Note
The steps in this article only apply to Outlook add-ins that run in classic Outlook on Windows. This is because classic Outlook on Windows uses a JavaScript file, while Outlook on Mac, on the web, and new Outlook on Windows use an HTML file that references the same JavaScript file. To learn more, see Configure your Outlook add-in for event-based activation and Implement an integrated spam-reporting add-in.
List allowed add-ins in a well-known URI
To list which add-ins are allowed to work with SSO or CORS, create a JSON file that identifies each JavaScript file for each add-in. Then, host that JSON file at a well-known URI. A well-known URI allows the specification of all hosted JS files that are authorized to obtain tokens for the current web origin. This ensures that the owner of the origin has full control over which hosted JavaScript files are meant to be used in an add-in and which ones are not, preventing any security vulnerabilities around impersonation, for example.
The following example shows how to configure SSO or CORS for two add-ins (a main version and beta version). You can list as many add-ins as necessary depending on how many you provide from your web server.
{
"allowed":
[
"https://addin.contoso.com:8000/main/js/autorun.js",
"https://addin.contoso.com:8000/beta/js/autorun.js"
]
}
Host the JSON file under a location named .well-known in the URI at the root of the origin. For example, if the origin is https://addin.contoso.com:8000/, then the well-known URI is https://addin.contoso.com:8000/.well-known/microsoft-officeaddins-allowed.json. For clarification, this file is to be hosted in your Office Web Add-in, not the web server that you're attempting to make a CORS request to. See the Outlook-Add-in-SSO-events sample for an example using the recommended location.
The origin refers to a pattern of scheme + subdomain + domain + port. The name of the location must be .well-known, and the name of the resource file must be microsoft-officeaddins-allowed.json. This file must contain a JSON object with an attribute named allowed whose value is an array of all JavaScript files authorized for SSO for their respective add-ins.
After you configure the well-known URI, if your add-in implements SSO, you can then call the getAccessToken() API to get an access token with the user's identity.
Important
While OfficeRuntime.auth.getAccessToken and Office.auth.getAccessToken perform the same functionality of retrieving an access token, we recommend calling OfficeRuntime.auth.getAccessToken in your event-based or spam-reporting (preview) add-in. This API is supported in all Outlook client versions that support event-based activation, integrated spam reporting, and SSO. On the other hand, Office.auth.getAccessToken is only supported in classic Outlook on Windows starting from Version 2111 (Build 14701.20000).