This post is as per beta version, there could be some changes with RTM version.
Authentication, authorization, and security in SharePoint 2013
What's new in SharePoint 2013 for authentication, authorization, and security
The following are some of the enhancements added to SharePoint 2013 Preview:
What's new in authentication for SharePoint 2013 Preview
SharePoint 2013 Preview includes improvements in claims infrastructure and authentication features that enable new server-to-server and app authentication scenarios.
SharePoint 2013: Claims is the new black
In SharePoint 2010, we had to choose between two options when creating a Content Web Application - to use Classic mode Authentication or Claims-based Authentication. Now in SharePoint 2013, Claims-based authentication mode is the default authentication method. You cannot from the web interface create content web applications using Classic mode. Classic-mode authentication is deprecated and can be managed only by using Windows PowerShell.
The app authentication and server-to-server authentication features of SharePoint 2013 Preview require claims-based authentication along with a lot of other features.
Plan authentication in SharePoint 2013 Preview
Find resources about user authentication, server-to-server authentication, and app authentication to help you understand and plan for authentication in SharePoint 2013 Preview.
Configure SAML-based claims authentication with ADFS in SharePoint 2013 Preview
Describes the steps to configure Security Assertion Markup Language (SAML)-based claims authentication using Active Directory Federation Services (AD FS) 2.0.
Configure forms-based authentication for a claims-based web application in SharePoint 2013 Preview
Describes the steps to configure forms-based authentication using a Lightweight Directory Access Protocol (LDAP) membership provider.
Configure server-to-server authentication in SharePoint 2013 Preview
Provides steps to configure server-to-server (S2S) authentication with another server that uses the S2S protocol.
Initial deployment administrative and service accounts in SharePoint 2013
Information about the administrative and service accounts that are required for an initial SharePoint 2013 deployment.
People Picker and claims providers overview (SharePoint 2013)
Get an overview of People Picker and links to topics about how to plan for People Picker in SharePoint 2013.
Report Where and How SharePoint Users Have Been Granted Access
This script produces a text file report of which items have been unique secured and which Active Directory users and groups have been granted access, based on the user domain specified. The report details whether the user or group has been granted rights directly, or if the user has been granted rights by membership to a SharePoint group though it does not identify if a user has been granted rights based on their membership to an AD Group which in turn has been added to a SharePoint group.
How to: Deploy a claims provider in SharePoint 2013
Learn how to deploy a SharePoint 2013 claims provider by using the features infrastructure