CalDAV

CalDAV
Name	CalDAV
Developer	Internet Engineering Task Force
Released	2007
Latest release	RFC 4791
Genre	Scheduling, calendar access

CalDAV

CalDAV is an Internet standard protocol for calendar access and scheduling that extends WebDAV and HTTP to manage iCalendar data, standardized by the Internet Engineering Task Force in RFC 4791 and adopted across enterprise and consumer services. It enables calendar clients to create, retrieve, update, and delete events on remote servers and to support shared calendars for organizations such as Google, Apple Inc., Microsoft Corporation, and academic institutions like MIT and Stanford University. Developed alongside complementary efforts like CardDAV and influenced by work within the IETF Calendaring and Scheduling Working Group, CalDAV has been integrated into projects including DAViCal, Radicale, Nextcloud, and cloud services used in environments from NASA to municipal administrations.

Overview

CalDAV builds on the foundation of HTTP methods and the WebDAV extensions originally specified in RFC 4918 to store and manipulate calendaring objects formatted as iCalendar components. The protocol is widely used by vendors such as Apple Inc., Google, Mozilla Foundation, and Microsoft Corporation to provide synchronization between servers and clients including Outlook (Microsoft), Apple Calendar, Mozilla Thunderbird, and mobile platforms like Android and iOS. Adoption spans commercial providers such as FastMail and Yahoo! as well as open-source projects like Kolab and Zimbra, and it intersects with authentication frameworks maintained by groups including IETF and the OpenID Foundation.

Protocol and Architecture

CalDAV specifies collection-oriented storage where each calendar is represented as a WebDAV collection and each event as an iCalendar resource, leveraging HTTP verbs such as GET, PUT, DELETE, and REPORT defined in RFC 7231 and WebDAV's extensions from RFC 4918. The architecture supports calendar discovery via service documents as in RFC 5789 and synchronization mechanisms similar to those in CardDAV and CalDAV Scheduling Extensions; deployments often integrate with directory services like LDAP and identity providers such as Microsoft Active Directory or Okta. Server implementations may use database backends like PostgreSQL, MySQL, or SQLite, and interact with mail systems like Postfix or Exim to handle scheduling notifications in accordance with standards from the IETF and implementations by vendors including Zimbra and CommuniGate Pro.

Authentication and Security

CalDAV commonly reuses HTTP authentication schemes such as Basic access authentication, Digest access authentication, and OAuth 2.0 as promoted by organizations like the OpenID Foundation; enterprise deployments often employ Kerberos or integration with SAML providers from vendors like Microsoft Corporation and Okta. Transport layer security is typically provided by TLS and certificates issued by authorities such as Let's Encrypt and DigiCert, while access control leverages WebDAV ACL extensions and directory-based permissions managed in systems like Microsoft Active Directory and OpenLDAP. Security considerations include cross-origin policies discussed by the W3C and threat models addressed in work by ENISA and the IETF security working groups, with server projects such as DAViCal and Radicale publishing hardening guides.

Implementations and Server Software

Notable server implementations include commercial products like Zimbra, Microsoft Exchange (through interoperability layers), and hosted providers including Google Workspace and FastMail, as well as open-source servers such as DAViCal, Radicale, Baïkal, Nextcloud, Kolab Groupware, and SOGo. Academic and research institutions such as CERN and University of Oxford have deployed CalDAV servers integrated with authentication systems like Shibboleth and storage backends such as PostgreSQL. Integration with collaboration suites from Atlassian and hosting platforms like DigitalOcean and Amazon Web Services is common; community projects maintained on platforms like GitHub and GitLab continue to evolve adapters and plugins.

Client Support and Interoperability

CalDAV is supported by client software including Apple Calendar, Mozilla Thunderbird with Lightning (calendar extension), Evolution (software), KOrganizer, and many mobile clients on iOS and Android that synchronize via servers operated by Google, Nextcloud, and hosting providers. Interoperability testing events and compatibility matrices have been coordinated by organizations such as the IETF and community efforts hosted on GitHub and forums including Stack Overflow, with middleware adapters provided by projects like DAVx⁵ for Android and synchronization bridges used by enterprise vendors such as Microsoft Corporation and Zimbra.

Extensions and Related Standards

Extensions and related standards include CalDAV Scheduling Extensions (RFC 6638), CardDAV for contact synchronization, CalDAV auto-configuration schemes used by Apple Inc. and Mozilla Foundation, and related calendaring formats such as iCalendar (RFC 5545). Integration points touch authentication and authorization standards like OAuth 2.0, SAML 2.0, and identity federation initiatives such as eduGAIN; calendaring workflow and interoperability are further shaped by specifications and guidelines from the IETF, W3C, and industry consortia including the Open Mobile Alliance.

Category:Internet Standards