Troubleshooting Authorization Failures In Claims-Based Sharepoint Authentication

Common Causes of Authorization Errors

When using claims-based authentication in SharePoint, users may encounter authorization errors that prevent them from accessing sites and content. There are several common causes for these authorization failures:

Expired Tokens

SharePoint uses security tokens to verify a user’s identity and authorization. These tokens eventually expire and need to be renewed for continued access. Expired tokens are a prevalent source of authorization errors in claims-based SharePoint deployments.

Invalid Tokens

In some cases, SharePoint authentication tokens become invalid before their expiration. This can happen due to changes in user permissions, password resets, or encryption issues. Attempting to access SharePoint with an invalid token will trigger authorization errors.

Permission Issues

Even with a valid access token, users may still encounter authorization failures if they lack the necessary permissions to access a site or content. Permission issues must be debugged at the user, group, or policy level in SharePoint and Active Directory.

Incorrect Authentication Method

If SharePoint is not configured properly to use claims-based authentication, users will receive authorization or access denied errors. Confirming the proper authentication mode is enabled is key.

Investigating Expired and Invalid Tokens

Diagnosing authorization failures often starts with inspecting the user’s SharePoint access token to check for expiration or invalidation issues:

How to Check Token Expiration Dates

The expiration date for access tokens is encoded in the JWT or other identity token format. Here are steps to inspect and decode the token to view the expiration time:

1. Obtain the user’s access token through the SharePoint REST API or SDK
2. Paste the token at jwt.ms to decode and inspect the payload
3. Check the “exp” claims value, which is a Unix timestamp of the expiration time
4. Convert the timestamp to your local date and time

Renewing Expired Tokens

If an access token has expired, a new one must be obtained by re-authenticating the user through the original OAuth or OpenID Connect flow. This allows SharePoint to mint a fresh access token without requiring the user’s password again. Example code:

  POST https://login.microsoftonline.com/{tenant}/oauth2/token
  Content-Type: application/x-www-form-urlencoded

  client_id=5731de76-14a6-49ae-97bc-6eba6914391e
  &scope=user.read mail.read  
  &refresh_token=CwyAAAWoL...
  &grant_type=refresh_token
  &client_secret=Pimq7Yo9b...

Debugging Invalid Tokens

If an access token is invalidated before its expiry time, a new token must be re-issued to the user. Causes for early invalidation include password changes, revoked OAuth consent, and changes to group membership or roles. Check the SharePoint and Azure AD audit logs to determine why existing tokens were invalidated.

Debugging Permission Issues

Valid claims-based access tokens will still fail authorization if SharePoint determines the user lacks permissions. Troubleshooting involves inspecting user permissions and adjusting as needed:

Viewing User Permissions

In the SharePoint admin center, search for the affected user and inspect their permission levels for the site in question. This shows all explicit and inherited permissions.

Granting Additional Permissions

If needed, locate the user or group in SharePoint and edit their permissions to allow additional access to the protected sites and content.

Revoking Unnecessary Permissions

Audit all user and group permissions and remove any unnecessary access to enforce principle of least privilege. Reduced scopes can improve security.

Configuring Appropriate Authentication

Flawed configuration of SharePoint authentication can also lead to authorization errors for valid users. Ensure claims-based authentication is properly set up:

Choosing Authentication Methods

SharePoint provides multiple authentication options including Windows/Kerberos, forms-based, and claims-based protocols. Choose the method that aligns with your account store and security standards.

Setting Up Claims-Based Authentication

For claims-based auth, SharePoint must federate with a trusted STS like Azure AD using WS-Fed, SAML, or OAuth/OpenID Connect standards. Carefully follow setup instructions.

Transitioning From Classic to Claims-Based

When converting a classic SharePoint deployment to claims-based authentication, be sure to thoroughly test and verify all functionality for users before rolling out.

Example Code for Renewing Tokens

POST https://login.microsoftonline.com/{tenant}/oauth2/token
Content-Type: application/x-www-form-urlencoded 

client_id=6731de76-14a6-49ae-97bc-6eba6914391e  
&scope=user.read%20mail.read
&code=OAAABAAAAiL9Kn2Z27UubvWFPbm0gLWQJVzCTE9UkP3pSx1aXxUjq3n8b2JRLk4OxVXr...   
&redirect_uri=http%3A%2F%2Flocalhost%2Fmyapp%2F
&grant_type=authorization_code
&client_secret=JqQX2PNo9bpM0uEihUPzyrh