OpenID Connect DNS-based Discovery
draft-sanz-openid-dns-discovery-00
The information below is for an old version of the document.
| Document | Type |
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| Authors | Vittorio Bertola , Marcos Sanz | ||
| Last updated | 2017-10-18 | ||
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draft-sanz-openid-dns-discovery-00
Network Working Group V. Bertola
Internet-Draft Open-Xchange
Intended status: Informational M. Sanz
Expires: April 21, 2018 DENIC eG
October 18, 2017
OpenID Connect DNS-based Discovery
draft-sanz-openid-dns-discovery-00
Abstract
The following document describes a DNS-based mechanism for a client
to discover an OpenID Identity Provider given an Identifier of the
End-User, as a complementary alternative to the existing WebFinger-
based mechanism.
Status of This Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on April 21, 2018.
Copyright Notice
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document authors. All rights reserved.
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1. Introduction
"OpenID Connect Discovery 1.0" [OpenID.Discovery] uses WebFinger
[RFC7033] to locate the OpenID Provider for an End-User in a process
called "issuer discovery". While this mechanism has been in place
for quite some time now and it has proven to work, it presents some
operational inconveniences: A (dedicated) WebFinger service has to be
setup and operated on top of an HTTPS server. Furthermore: in an
OpenID deployment with distributed resources, each resource would
have to be running its own WebFinger service to point to its issuer.
This presents scaling/operating challenges, especially in a scenario
where the deployment happens at Internet scale and each resource may
use a different, personal domain name.
This document presents a lightweight discovery mechanism based on top
of DNS (and DNS has to be setup anyway for the WebFinger approach to
work). This so-called "DNS-based discovery" does not disrupt the
existing discovery specification and is presented as an alternative
discovery process, compatible to the existing issuer discovery
process described in "OpenID Connect Discovery 1.0"
[OpenID.Discovery] if interpreted as a so-called "out-of-band"
mechanism.
Additionally the mechanisms described in this document enrich the
discovery process by allowing to discover not only the issuer, but
also potential Claims Providers [OpenID.Core] available for a given
End-User identifier.
2. Requirements Notation and Conventions
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].
Throughout this document, values are quoted to indicate that they are
to be taken literally. When using these values in protocol messages,
the quotes MUST NOT be used as part of the value.
3. DNS-based Discovery Resource Record
The format defined here has been inspired by the DMARC [RFC7489] and
DKIM [RFC6376] specifications and some text passages have been
directly copied from those standards to allow for a reading without
following references.
DNS-based discovery metadata are stored as DNS TXT records in
subdomains named "_openid". The underscore construct is used to
define a semantic scope for DNS records that are associated with the
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parent domain (s. "DNS Scoped Data Through Global '_Underscore'
Naming of Attribute Leaves" [I-D.ietf-dnsop-attrleaf]).
For example, the domain owner of "myname.example.com" would post
OpenID configuration in a TXT record at "_openid.myname.example.com".
This DNS-located OpenID metadata will hereafter be called the "OpenID
record".
To allow for the use of e-mail addresses as resources, the following
additional rules are defined:
o In case the resource identifier contains at least one "@"
character, the rightmost "@" character is replaced by the string
"._openidemail.", which introduces an additional DNS subdomain
inside the identifier's domain name.
o If any character in the resulting resource identifier is
disallowed from use in domain names as per [RFC1035] section
2.3.1, the punycoding algorithm defined in [RFC3492] is applied.
Per [RFC1035] a TXT record can comprise several "character-string"
objects. Where this is the case, the evaluator of the OpenID record
must concatenate these strings by joining together the objects in
order and parsing the result as a single string.
Content of OpenID records follow the extensible "tag=value" syntax
for DNS-based key records defined in [RFC6376] and definition there
applies. Specifically:
o Values are a series of strings containing either plain text or
"base64" text (as defined in [RFC2045], Section 6.8). The
definition of the tag will determine the encoding of each value.
o Unencoded semicolon (";") characters must not occur in the value,
since that separates tag-value pairs.
o Whitespaces are allowed anywhere around tags. In particular, any
whitespace after the "=" and any whitespace before a terminating
";" is not part of the value; however, whitespace inside the value
is significant.
o Tags must be interpreted in a case-sensitive manner. Values must
be processed as case sensitive unless the specific tag description
of semantics specifies case insensitivity. Host and domain names
in this context are to be compared in a case insensitive manner,
per [RFC4343].
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o Tags with duplicate names must not occur within a single tag-list;
if a tag name does occur more than once, the entire tag-list is
invalid.
o Tag=value pairs that represent the default value for optional
records may be included to aid legibility.
o Unrecognized tags must be ignored.
o Tags that have an empty value are not the same as omitted tags.
An omitted tag is treated as having the default value; a tag with
an empty value explicitly designates the empty string as the
value.
Only tags defined in this document or in later extensions are to be
processed; note that given the rules of the previous paragraph,
addition of a new tag into the registered list of tags does not
itself require a new version of OpenID record to be generated (with a
corresponding change to the "v" tag's value, see later), but a change
to any existing tags does require a new version.
The following tags are introduced as the initial valid OpenID tags:
o v: Version (plain-text; REQUIRED). Identifies the record
retrieved as a OpenID record. It must have the value of "OID1".
The value of this tag must match precisely; if it does not or it
is absent, the entire record must be ignored. It must be the
first tag in the list.
o iss: The designated hostname for the Issuer (plain-text;
REQUIRED). Internationalized domain names must be encoded as
A-labels, as described in Section 2.3 of [RFC5890]. That hostname
can be used as the issuer location of an OpenID Connect Discovery
1.0 (Section 4) Configuration Request to discover its relevant
OpenID endpoints. The issuer can contain path components (e.g.
"issuer.example.com/path").
o clp: The designated hostname for the Claims Provider (plain-text;
OPTIONAL). Internationalized domain names must be encoded as
A-labels, as described in Section 2.3 of [RFC5890]. That hostname
can be used by Identity Providers as a claim source for aggregated
or distributed claims. Support for Aggregated Claims and
Distributed Claims is OPTIONAL in the OpenID Core specification,
so is the usage of this tag. The value of this tag can contain
path components (e.g. "provider.example.com/path").
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The following is an example of a valid OpenID record for the domain
example.com according to this specification:
_openid IN TXT "v=OID1;iss=auth.freedom-id.de;clp=identityagent.de"
Figure 1: Example OpenID record
4. DNS-based Issuer Discovery Process
DNS-based OpenID Provider Issuer discovery is the process of
determining the location of the OpenID Provider with this
specification.
DNS-based issuer discovery requires the following information to make
a discovery request:
o resource - Identifier for the target End-User that is the subject
of the discovery request
o host - Hostname target of the discovery DNS query
To start discovery of OpenID endpoints, the End-User supplies an
Identifier to the Relying Party. The RP applies the same
normalization rules to the Identifier as described in "OpenID Connect
Discovery 1.0" [OpenID.Discovery] to determine the Resource and Host.
It is worth mentioning that as result of those rules the resource
could exactly match the host (e.g. resource is "example.com" and host
is "example.com").
The RP will then follow the following lookup scheme:
1. The RP queries the DNS for an OpenID record at host. A possibly
empty set of records is returned.
2. Records that do not start with a "v=" tag that identifies the
current version of this document, or an older version of this
document supported by the RP, are discarded. If a tag
identifying the current version is found, all records identifying
other versions are discarded. If no tag identifying the current
version is found, but other tags identifying older versions are,
the records using the latest supported version are kept, and all
others are discarded.
3. If the remaining set contains multiple records or no records, the
DNS-based discovery process terminates.
4. If the retrieved OpenID record does not contain a valid iss tag,
the process terminates.
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5. Once the Issuer has been extracted from the iss tag, the regular
dynamic discovery process can be resumed in Section 4 "Obtaining
OpenID Provider Configuration Information" of [OpenID.Discovery].
As already mentioned in [OpenID.Discovery] it is also worth noting
that no relationship can be assumed between the user input Identifier
string and the resulting Issuer location.
5. Security Considerations
DNS-based discovery depends directly on the security of the DNS.
OpenID records must be ignored if not deployed in parallel with
DNSSEC [RFC4033]. DNSSEC validation of OpenID records MUST be
performed at all time before using them for any purpose. DNSSEC-
validation errors must result in abortion of this DNS-based discovery
process.
6. IANA Considerations
tbd
7. References
7.1. Normative References
[RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
November 1987, <https://www.rfc-editor.org/info/rfc1035>.
[RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part One: Format of Internet Message
Bodies", RFC 2045, DOI 10.17487/RFC2045, November 1996,
<https://www.rfc-editor.org/info/rfc2045>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC3492] Costello, A., "Punycode: A Bootstring encoding of Unicode
for Internationalized Domain Names in Applications
(IDNA)", RFC 3492, DOI 10.17487/RFC3492, March 2003,
<https://www.rfc-editor.org/info/rfc3492>.
[RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "DNS Security Introduction and Requirements",
RFC 4033, DOI 10.17487/RFC4033, March 2005,
<https://www.rfc-editor.org/info/rfc4033>.
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[RFC4343] Eastlake 3rd, D., "Domain Name System (DNS) Case
Insensitivity Clarification", RFC 4343,
DOI 10.17487/RFC4343, January 2006,
<https://www.rfc-editor.org/info/rfc4343>.
[RFC5890] Klensin, J., "Internationalized Domain Names for
Applications (IDNA): Definitions and Document Framework",
RFC 5890, DOI 10.17487/RFC5890, August 2010,
<https://www.rfc-editor.org/info/rfc5890>.
7.2. Informative References
[I-D.ietf-dnsop-attrleaf]
Crocker, D., "DNS Scoped Data Through Global '_Underscore'
Naming of Attribute Leaves", draft-ietf-dnsop-attrleaf-02
(work in progress), March 2017.
[OpenID.Core]
Sakimura, N., Bradley, J., Jones, M., de Medeiros, B., and
C. Mortimore, "OpenID Connect Core 1.0", November 2014,
<http://openid.net/specs/openid-connect-core-1_0.html>.
[OpenID.Discovery]
Sakimura, N., Bradley, J., Jones, M., and E. Jay, "OpenID
Connect Discovery 1.0", November 2014,
<http://openid.net/specs/
openid-connect-discovery-1_0.html>.
[RFC6376] Crocker, D., Ed., Hansen, T., Ed., and M. Kucherawy, Ed.,
"DomainKeys Identified Mail (DKIM) Signatures", STD 76,
RFC 6376, DOI 10.17487/RFC6376, September 2011,
<https://www.rfc-editor.org/info/rfc6376>.
[RFC7033] Jones, P., Salgueiro, G., Jones, M., and J. Smarr,
"WebFinger", RFC 7033, DOI 10.17487/RFC7033, September
2013, <https://www.rfc-editor.org/info/rfc7033>.
[RFC7489] Kucherawy, M., Ed. and E. Zwicky, Ed., "Domain-based
Message Authentication, Reporting, and Conformance
(DMARC)", RFC 7489, DOI 10.17487/RFC7489, March 2015,
<https://www.rfc-editor.org/info/rfc7489>.
Authors' Addresses
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Vittorio Bertola
Open-Xchange
Email: vittorio.bertola@open-xchange.com
URI: https://www.open-xchange.com
Marcos Sanz
DENIC eG
Kaiserstrasse 75 - 77
Frankfurt am Main 60329
Germany
Email: sanz@denic.de
URI: https://www.denic.de
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