Integrated Windows Authentication (IWA)

Integrated Windows Authentication (IWA) is Microsoft’s native mechanism for authenticating users to web or network resources using their existing Windows domain credentials. It enables passwordless single sign-on within trusted Active Directory environments, leveraging Kerberos (preferred) or NTLM protocols for secure challenge–response authentication.

Key Capabilities

• Seamless Windows SSO: Authenticates users automatically using their domain session credentials—no password re-entry required.

• Kerberos-based authentication: Uses Kerberos as the primary mode, supporting mutual authentication and delegated access through Service Principal Names (SPNs) and constrained delegation.

• Automatic NTLM fallback: Switches to NTLM when Kerberos is unavailable due to cross-domain or SPN configuration gaps.

• Broad compatibility: Supported by Microsoft IIS, .NET, and Java applications, and modern browsers like Edge, Chrome, and Firefox with domain join configurations.

Limitations

• Network dependency: Functions reliably only within trusted AD domains or VPN-connected networks; not suited for internet-facing or cross-forest SaaS use.

• Configuration sensitivity: Requires proper browser and server policy setup (e.g., trusted sites, AuthServerWhitelist) for seamless login.

• No federation or modern tokens: IWA does not issue SAML or OIDC tokens; external federation via ADFS or Microsoft Entra ID is required for web or cloud scenarios.

• MFA gap: Multi-factor authentication is not inherent to IWA and must be layered through conditional access or federated IdPs.

• Windows dependency: Optimized for Windows and Active Directory ecosystems; non-Windows clients need Kerberos libraries or alternative methods.