Troubleshooting Authentication Errors When Using Javascript With Sharepoint Online
Common Causes of Authentication Errors
When using JavaScript to access the SharePoint Online REST APIs or other resources, developers may encounter various authentication-related errors that prevent successful requests. Understanding the common causes of these authentication errors can help troubleshoot and resolve issues.
Expired Access Tokens
SharePoint Online uses OAuth access tokens to authenticate and authorize API requests. These JSON web tokens have a expiration time limit, usually around one hour. Once expired, the access tokens will no longer allow the bearer to access SharePoint resources. Requesting new access tokens is required to re-establish authenticated access.
Cross-Domain Access Issues
Standard web browser security restricts JavaScript code from making AJAX requests to domains other than the originating domain. Since SharePoint Online has a different domain than most sites hosting front-end code, cross-domain HTTP requests can be blocked. Enabling CORS or using a cross-domain library is necessary for these inter-domain requests.
Incorrect Permission Scopes
The OAuth access tokens provided by SharePoint also contain encoded permission scopes that determine what resources and APIs the client code has access to. If the scopes do not match the API or features being accessed, authorization errors can occur. Auditing the required scopes and ensuring access tokens match those requirements will prevent many issues.
Diagnosing the Authentication Error
Determining the specific cause of a SharePoint Online authentication error is important for selecting the proper resolution approach. Developers can leverage browser tools, network inspection, and SharePoint permissions checking to diagnose the failed requests.
Check Browser Console for Error Messages
Most authentication failures will log descriptive errors to the browser console containing status codes and messages indicating the type of issue. These console messages should indicate whether failure is due to invalid tokens, CORS problems, incorrect permission scopes, or other causes. Console output provides the starting point for troubleshooting the problem.
Inspect Network Requests for Status Codes
Browser developer tools also allow inspection of the raw HTTP requests made to SharePoint OAuth or API endpoints. The response headers and status codes provide additional insight into the type of authentication error experienced. Status codes like 401, 403, or CORS errors indicate the general reason for request failure.
Verify User Permissions and Access Token Scopes
Using the SharePoint admin center, developers can check that the user account and OAuth client have been granted the necessary API permissions for access token scope requests. Or consult code to ensure the JavaScript requests the scopes matching those assigned permissions prior to making API calls. Mismatched scopes lead to authorization failed responses.
Fixing Expired Access Tokens
An authentication error due to expired OAuth access tokens requires requesting new valid tokens from SharePoint to regain access to resources. This can be achieved automatically or through manual means in client JavaScript code.
Implement Automatic Token Refreshing
The most robust way to prevent access token expiration is to automatically refresh them prior to expiry time using refresh tokens. Refresh tokens allow acquiring new access tokens without re-prompting the user to log in. By calculating expiry and requesting refreshed tokens, applications avoid authentication errors.
Manually Request New Access Tokens
If handling token expiry through refresh tokens is not implemented, developers must catch authentication failed errors in code and make new token requests. By getting the user to reauthenticate and authorizing new tokens, access is regained for future API calls. This method is more labor-intensive than refresh workflows.
Enabling Cross-Domain Access
Due to standard web browser security restrictions, making JavaScript requests from the domain hosting front-end code to the SharePoint domain can fail with cross-origin errors. CORS and cross-domain proxies or libraries can resolve this.
Configure CORS in SharePoint Admin Center
The SharePoint admin center provides options for enabling Cross-Origin Resource Sharing (CORS) for hosted sites and assets. Adding the domain of front-end code to the CORS whitelists enables those external pages to directly access SharePoint resources cross-domain.
Use Cross-Domain Library for Requests
Rather than configuring CORS, client code can instead use a JavaScript proxy library to avoid cross-origin restrictions. Making domain requests through libraries like JSONP proxies or Fetch overcomes default browser security policies. This method works around CORS requirements at the code level.
Setting Correct Permission Scopes
If using SharePoint API access token scopes not matching granted user permissions, authorization failed errors result. Fixing requires proper scope mapping to assigned permissions.
Request Appropriate Scopes for API Access
When using authorization codes or implicit grant flows to obtain access tokens, ensure the requested scopes match the target SharePoint Online APIs or resources being accessed. Assign permissions to those scopes at the user and application level to allow correct authorization.
Audit Permission Requirements for Site Resources
Compare user account permissions and OAuth client application permission settings against the access levels needed for site assets and REST APIs being accessed. Adjust configurations to ensure alignment between permission grants and token scope requests made by client JavaScript code.
Example Code for Handling Auth Errors
Sample JavaScript code snippets below demonstrate common techniques for handling authentication errors when working with the SharePoint Online REST APIs from front-end code.
Try/Catch for Handling Token Expiration
“`js
try {
let response = await fetch(sharepointResource, {
headers: {
Authorization: `Bearer ${accessToken}`
}
});
// process response
} catch (error) {
// check for 401 status
if (error.response.status === 401) {
// refresh expired token
accessToken = await refreshAccessToken();
} else {
// handle other errors
}
}
“`
Wrapping AJAX Calls to Enable CORS
“`js
function crossDomainGet(url) {
// proxy AJAX request through CORS proxy
return fetch(‘https://cors-proxy.example.com/’ + url, {
method: ‘GET’
})
.then(response => response.json());
}
let data = await crossDomainGet(sharepointSiteUrl);
“`
Getting Access Token with Required Scopes
“`js
async function getToken() {
return await fetch(‘/token’, {
method: ‘POST’,
body: {
// request scopes for SharePoint API
scopes: [
‘https://graph.microsoft.com/Sites.Read.All’,
‘https://graph.microsoft.com/Files.Read.All’
]
}
})
.then(response => response.accessToken);
}
“`
