Authentication in Windows API

Authentication is the process of verifying the identity of a user, device, or service before granting access to system resources. Windows provides several APIs and mechanisms to perform secure authentication, ranging from legacy protocols to modern token‑based solutions.

Core Authentication APIs

• LogonUser – Authenticates a user by username and password and returns a token.
• AcquireCredentialsHandle – Retrieves a handle to a set of credentials for use with SSPI.
• InitializeSecurityContext – Initiates or continues the client side of a security handshake.
• AcceptSecurityContext – Completes the server side of a security handshake.

Sample: Using LogonUser

// C++ example using LogonUser
#include <windows.h>
#include <stdio.h>

int main()
{
    HANDLE hToken = NULL;
    BOOL ok = LogonUser(
        L"username",      // user name
        L"DOMAIN",        // domain or local computer
        L"Password123!", // password
        LOGON32_LOGON_INTERACTIVE,
        LOGON32_PROVIDER_DEFAULT,
        &hToken);

    if (ok) {
        wprintf(L"Logon successful! Token: %p\n", hToken);
        CloseHandle(hToken);
    } else {
        wprintf(L"Logon failed. Error: %lu\n", GetLastError());
    }
    return 0;
}

Modern Alternatives

For cloud‑first applications and services, consider using:

• Microsoft Identity Platform (MSAL) – OAuth2 / OpenID Connect flows.
• Windows Hello for Business – Biometrics and PIN.
• Credential Guard – Isolates the LSASS process.

Related Topics

• Authorization
• Cryptography
• Security Policy

Discussion

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