ADFS Authentication Types
AD FS 2.0, out of the box, supports four local authentication types. By default AD FS 2.0 Federation Servers use Integrated Windows Authentication (IWA) and AD FS 2.0 Federation Server Proxy servers use Form-Based Authentication (FBA). The reason for this is that you would prefer no credential prompt for your internal users who can directly contact your internal Federation Servers, and users who are coming from the internet via the Federation Server Proxy servers would not be able to experience integrated Windows authentication, thus a customizable forms-based page is the best fit.
Integrated Windows authentication (IWA)
Integrated Windows authentication (IWA) - can utilize Kerberos or NTLM authentication. You should always prefer Kerberos authentication over NTLM and configure the appropriate service principal name (SPN) for the AD FS 2.0 service account so that Kerberos can be used. Credential collection can happen in two ways depending on how your browser is configured:
- automatic logon with current user name and password - used when AD FS 2.0 URL is in IE Intranet Zone or another IE Zone which is configured to automatically logon with current user name and password
- Browser-based HTTP 401 authentication prompt - used when credentials cannot be automatically supplied to the 401 challenge for credentials
Forms-based authentication (FBA)
Forms-based authentication (FBA) - A forms-based .aspx page is presented to the user containing username and password fields. This page is fully customizable so that you can add new sign-in logic or page customizations (logos, style sheet, etc.)
Transport layer security client authentication
Transport layer security client authentication - a.k.a. Client certificate authentication or Smart Card authentication. The credential is supplied by selecting an appropriate client authentication certificate.
Basic authentication - The web browser displays a credential prompt and the credentials supplied are sent across the network. The advantage of Basic authentication is that it is part of the Hypertext Transfer Protocol (HTTP) specification, and is supported by most browsers. The disadvantage is that Web browsers that use Basic authentication transmit passwords in an unencrypted form. If a non-user monitors communications on your network, they can easily intercept and decipher these passwords by using publicly available tools. Therefore, Basic authentication is not recommended unless you are confident that the connection between the user and your Web server is secure; direct cable connections or a dedicated lines are secure connections.
ADFS with Windows 2012 R2 example