Securing Sharepoint Online Authentication With Javascript: Security Considerations
Understanding SharePoint Online Authentication
SharePoint Online uses various authentication methods to verify user identities and enable secure access to resources. Common authentication options include OAuth 2.0 and OpenID Connect flows, integrated Windows authentication, and forms-based authentication.
These authentication mechanisms can contain vulnerabilities if not properly implemented. Attackers may attempt to intercept tokens, exploit configuration issues, leverage insecure endpoints, or obtain user credentials. Thus securing authentication code is critical for SharePoint Online security.
JavaScript plays an integral role in SharePoint Online authentication on the front-end. Properly coding sign-in, token handling, and API call authorization in JavaScript can help mitigate common authentication attack vectors and keep SharePoint data safe from unauthorized access.
Overview of Authentication Methods in SharePoint Online
SharePoint Online supports standard OAuth 2.0 and OpenID Connect authentication flows for cloud-based identity management. The authorization code grant leverages an Azure AD tenant for identity and access control. Forms-based authentication can also be enabled for intranet sites.
Integrated Windows authentication uses Kerberos or NTLM to automatically sign in users against on-premises Active Directory. Users don’t reenter credentials, providing a seamless authenticated experience in SharePoint hybrid or federated environments.
Common Vulnerabilities in SharePoint Online Authentication
Vulnerabilities often arise from misconfigured authentication settings or coding oversights:
- Weak client-side token handling exposing tokens
- Overly broad token scopes and permissions
- Lack of token validation on the backend after initial authentication
- Using weak hashing or encoding for stored credentials in custom auth implementations
Attackers can steal exposed tokens to impersonate legitimate users. They can also exploit vulnerabilities to escalate privileges or access protected resources by tampering with tokens or authentication logic.
Importance of Properly Securing Authentication
SharePoint Online stores sensitive documents, data, and business logic. Compromised authentication exposes organizations to data theft, credential harvesting, malware injections, CSRF attacks, business disruption through ransomware, and more.
JavaScript plays a pivotal role in front-end authentication workflows. Adhering to identity management best practices in JavaScript can prevent the most common authentication attack paths seen in SharePoint environments.
Implementing Secure Authentication with JavaScript
JavaScript can implement robust authentication securely by leveraging libraries, registering clients properly, requesting adequate tokens, refreshing expired tokens, and storing tokens safely on the client.
Using Libraries like msal.js for Authentication
The Microsoft Authentication Library for JavaScript (msal.js) provides an easy interface for integrating with Azure AD identity and OAuth token flows:
- Easily request and refresh OAuth tokens
- Single sign-on across apps sharing the login authority
- Integrated token caching and management
- Built-in protection against common attacks
Using a vetted library like msal.js prevents having to build custom token handling from scratch.
Registering Client Applications Securely
Registered OAuth client apps hold credentials that can be misused if compromised. Follow secure registration practices:
- Register clients securely from the Azure AD admin portal
- Generate a secure app secret during registration
- Enable client credential authorization flows for server-side clients
Registering clients properly prevents listing apps under user control that could be silently consented to by attackers for token theft.
Requesting Tokens and Scopes Securely
Always request the most restricted scopes necessary. Only require read scopes if no write operations are performed. Request additional scopes only when needed for specific operations to limit exposure of underlying APIs and data.
Encapsulate token acquisition into a dedicated authentication service module to centralize the security sensitive logic.
Refreshing Tokens Properly
Ensure a valid token exists before calling protected SharePoint endpoints. Check expiresOn timestamps on access tokens:
- Refresh close-to-expiring tokens to allow uninterrupted access to resources
- Refresh tokens silently without redirecting the user when possible
- Prompt for user context only when silent token refresh fails
Silent token refresh prevents unnecessary interruption of user workflows due to expired sessions.
Storing Tokens Securely
Avoid leakage of tokens to logs, network transmissions, or the client DOM. Consider security when persisting tokens on the client:
- Store tokens in memory without serialization to reduce leakage risks
- Use sessionStorage instead of localStorage if persisting tokens
- Set the
secureflag on tokens stored in cookies
Always treat access tokens as short-lived credentials to limit damage from exposed tokens.
Code Examples for Secure Authentication
Properly coding authentication logic is key for SharePoint Online security. Below are examples of secure JavaScript token operations.
Initializing msal.js Correctly
// Initialize msal.js with registered application coordinates
const msalConfig = {
auth: {
clientId: "12345678-1234-1234-1234-123456789abc",
authority: "https://login.microsoftonline.com/contoso.onmicrosoft.com"
}
};
const msalInstance = new PublicClientApplication(msalConfig);
Requesting a Token with Proper Scopes
async function getToken() {
const tokenRequest = {
scopes: ["Sites.Read.All"]
};
return await msalInstance.acquireTokenSilent(tokenRequest);
}
Refreshing an Expired Token
async function refreshToken() {
if (isTokenExpired(storedToken)) {
const refreshedToken =
await msalInstance.acquireTokenSilent(storedToken.scopes);
return refreshedToken;
}
}
Storing a Token in sessionStorage
function storeToken(token) {
sessionStorage.setItem("sp_token", JSON.stringify(token));
}
Avoiding Common Authentication Pitfalls
Certain authentication anti-patterns frequently surface in SharePoint security assessments. Be sure to avoid:
Not Validating Tokens on the Backend
Validate tokens on protected API endpoints by inspecting claims, signatures, and issuers. Never assume client-passed tokens have not been tampered with.
Allowing Insecure Flows like Implicit Grant
Avoid implicit grant flows that immediately expose access tokens in URLs. The authorization code grant with PKCE is most secure for SP Online integrations.
Exposing Tokens in Logs or Responses
Prevent token leakage to logs, network traffic, or client responses which could expose credentials. Follow token encryption best practices.
Reusing Refresh Tokens Forever
Rotate refresh tokens periodically or after high privilege operations by re-authenticating users. Limiting refresh token lifespan secures accounts.
Ongoing Best Practices for Authentication Security
Consistently follow identity management best practices across authentication infrastructure:
Enable Advanced Security Features
Utilize advanced identity protection in Azure AD to detect suspicious authentication patterns and potential identity compromises using machine learning.
Follow Identity and Access Guidelines
Govern access according to Microsoft and NIST identity management standards. Continuously optimize permission scopes and entitlements.
Audit and Pen-Test Authentication Regularly
Assess authentication endpoints for vulnerabilities frequently. Perform regular token reviews and inspection for visibility into how credentials flow through systems.
Stay Up-to-Date on Latest Security Notices
Monitor advisories for critical authentication vulnerabilities and updated remediation guidance. Rapidly patch security issues related to identity management.
