Network Working Group C. Daboo Internet-Draft Apple Inc. Expires: November 22, 2009 May 21, 2009 Use of SRV records for locating CalDAV calendar services draft-daboo-srv-caldav-00 Status of This Memo This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on November 22, 2009. Copyright Notice Copyright (c) 2009 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents in effect on the date of publication of this document (http://trustee.ietf.org/license-info). Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Abstract This specification describes how SRV records can be used to locate a CalDAV based calendar service. Daboo Expires November 22, 2009 [Page 1] Internet-Draft SRV for CalDAV May 2009 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Conventions Used in This Document . . . . . . . . . . . . . . . 3 3. CalDAV SRV service types . . . . . . . . . . . . . . . . . . . 3 4. CalDAV Client "Bootstrapping" . . . . . . . . . . . . . . . . . 3 5. Security Considerations . . . . . . . . . . . . . . . . . . . . 4 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5 7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 5 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 5 8.1. Normative References . . . . . . . . . . . . . . . . . . . 5 8.2. Informative References . . . . . . . . . . . . . . . . . . 6 Daboo Expires November 22, 2009 [Page 2] Internet-Draft SRV for CalDAV May 2009 1. Introduction [RFC2782] defines a DNS-based service discovery protocol that has been widely adopted as a means of locating particular services within a local area network and beyond, using SRV RR records. [RFC4791] defines the CalDAV Calendar Access protocol, based on HTTP [RFC2616], for accessing calendar data stored on a server. CalDAV clients need to be able to discover appropriate CalDAV servers within their local area network and at other domains. This specification defines new SRV service types for the CalDAV protocol, and gives an example of how clients can use this together with other protocol features to enable simple client configuration. 2. Conventions Used in This Document The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. 3. CalDAV SRV service types This specification adds two service types for use with SRV records: caldav: Identifies a CalDAV server that uses HTTP without transport layer security ([RFC2818]). caldavs: Identifies a CalDAV server that uses HTTP with transport layer security ([RFC2818]). Clients SHOULD honor "TTL", "Priority" and "Weight" values in the SRV records, as described by [RFC2782]. Example: service record for server without transport layer security _caldav._tcp SRV 0 1 80 calendar.example.com. Example: service record for server with transport layer security _caldavs._tcp SRV 0 1 443 calendar.example.com. 4. CalDAV Client "Bootstrapping" This section describes a procedure that CalDAV clients MAY use to do their initial configuration based on minimal user input. Minimal input from a user would consist of a calendar user address. Daboo Expires November 22, 2009 [Page 3] Internet-Draft SRV for CalDAV May 2009 A calendar user address is defined by iCalendar [I-D.ietf-calsify-rfc2445bis] to be a URI [RFC3986]. Provided a user identifier and a domain name can be extracted from the URI, this simple "bootstrap" configuration can be done. If the calendar user address is a "mailto:" [RFC2368] URI, the "mailbox" portion of the URI is examined and the "local-part" and "domain" portions extracted. The "local-part" is used for the user identifier and the "domain" is used as the service domain. If the calendar user address is an "http:" [RFC2616] or "https:" [RFC2818] URI, the "userinfo" and "host" portion of the URI is extracted. The "userinfo" is used for the user identifier and the "host" is used as the service domain. Once the user identifier and service domain have been extracted, the following is done: 1. An SRV lookup for _caldavs._tcp is done against the extracted service domain. 2. If no result is found for _caldavs._tcp, the client can try _caldav._tcp provided non-SSL connections are appropriate. 3. If an SRV record is returned the client extracts the server host name and port number 4. The client does an authenticated "PROPFIND" [RFC4791] request using the user identifier, host name and port number and a request URI of "/". The body of the request should include the DAV:current-user-principal [RFC5397] property as one of the properties to return. Note that clients MUST properly handle HTTP redirect response statuses for the request. 5. If the DAV:current-user-principal property is returned, the client uses the value for the principal-URI of the calendar user. Given that quantity, it can do a "PROPFIND" on the principal-URI and discover additional properties for configuration. 6. If the DAV:current-user-principal property is not returned, then the client will need to request the principal-URI path from the user in order to continue with configuration. 5. Security Considerations Clients that support transport layer security as defined by [RFC2818] SHOULD try the "caldavs" service first before trying the "caldav" service. If a user has explicitly requested a connection with Daboo Expires November 22, 2009 [Page 4] Internet-Draft SRV for CalDAV May 2009 transport layer security, the client MUST NOT use any service information returned for the "caldav" service. A malicious attacker with access to the DNS server data can potentially cause clients to connect to any server chosen by the attacker. In the absence of a secure DNS option, clients SHOULD check that the host name returned in the SRV record matches the original service domain that was queried. If the host is not in the queried domain, clients SHOULD verify with the user that the SRV host name is suitable for use before executing any CalDAV requests against the host. 6. IANA Considerations This document does not require any actions on the part of IANA. 7. Acknowledgments This specification was suggested by discussion that took place within the Calendaring and Scheduling Consortium's CalDAV Technical Committee. The authors thank the participants of that group for their input. The "bootstrapping" process is based on diagrams developed by Wilfredo Sanchez. 8. References 8.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC2368] Hoffman, P., Masinter, L., and J. Zawinski, "The mailto URL scheme", RFC 2368, July 1998. [RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999. [RFC2782] Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for specifying the location of services (DNS SRV)", RFC 2782, February 2000. [RFC2818] Rescorla, E., "HTTP Over TLS", Daboo Expires November 22, 2009 [Page 5] Internet-Draft SRV for CalDAV May 2009 RFC 2818, May 2000. [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform Resource Identifier (URI): Generic Syntax", STD 66, RFC 3986, January 2005. [RFC4791] Daboo, C., Desruisseaux, B., and L. Dusseault, "Calendaring Extensions to WebDAV (CalDAV)", RFC 4791, March 2007. 8.2. Informative References [I-D.ietf-calsify-rfc2445bis] Desruisseaux, B., "Internet Calendaring and Scheduling Core Object Specification (iCalendar)", draft-ietf-calsify-rfc2445bis-10 (work in progress), April 2009. [RFC5397] Sanchez, W. and C. Daboo, "WebDAV Current Principal Extension", RFC 5397, December 2008. Author's Address Cyrus Daboo Apple Inc. 1 Infinite Loop Cupertino, CA 95014 USA EMail: cyrus@daboo.name URI: http://www.apple.com/ Daboo Expires November 22, 2009 [Page 6]