If you want to authenticate users with Microsoft Active Directory (AD) without redirecting them to the Microsoft login page (i.e., without using OAuth or OpenID Connect redirection flows), you can achieve this using one of the following methods:

1. LDAP Authentication

Use LDAP (Lightweight Directory Access Protocol) to directly authenticate against your on-premises Active Directory.

How it works:

The user provides their username and password.

Your application communicates with AD over LDAP to validate credentials.

Steps:

1. Connect to your AD server (e.g., ldap://domaincontroller.example.com).

2. Bind using the provided credentials ([email protected] or DOMAIN\username).

3. If the bind succeeds, the credentials are valid.

Libraries/Tools:

For Node.js: ldapjs

For Python: ldap3

For .NET: System.DirectoryServices

Note: This approach requires secure communication (e.g., LDAPS) to protect credentials during transmission.

2. Active Directory Federation Services (ADFS) + Integrated Windows Authentication (IWA)

If users are part of the same intranet or domain, you can leverage Integrated Windows Authentication.

How it works:

The user's Windows credentials (via Kerberos or NTLM) are automatically used for authentication.

This avoids prompting for credentials entirely.

Setup:

1. Configure ADFS to support IWA.

2. Your backend verifies the Kerberos/NTLM tokens with AD.

Libraries/Tools:

Use the Negotiate/Kerberos authentication protocol in your server framework.

Limitation: Works best for intranet applications where users are domain-joined.

3. Microsoft Graph API with Service Account

Use the Microsoft Graph API to verify user credentials indirectly.

How it works:

Your app receives the username and password from the user.

Use a service account or app credentials to query Microsoft Graph and validate the user.

Steps:

1. Configure app registration in Azure AD.

2. Use Graph API's /users or /me endpoints to verify credentials indirectly.

Security Consideration: This is less common since it involves handling raw user credentials.

4. Direct Authentication via Secure Token Service (STS)

Query AD directly using tools like Secure Token Services or Kerberos tokens.

This can involve using a middle-layer authentication proxy, such as:

Windows Authentication with IIS.

Custom middleware that validates AD credentials.

Key Security Considerations:

TLS Encryption: Always secure communication with AD using LDAPS or HTTPS.

Password Handling: Never store or log raw passwords.

Least Privilege: Use service accounts with minimal privileges when querying AD.