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1 \documentclass[11pt,a4paper]{ivoa}
2 \input tthdefs
4 \usepackage{listings}
5 %\lstloadlanguages{sh,make,xml,[latex]tex}
6 \lstset{flexiblecolumns=true,numberstyle=\small,showstringspaces=False,
7 identifierstyle=\texttt,defaultdialect=[latex]tex,language=tex}
10 \title{IVOA Single-Sign-On Profile: Authentication Mechanisms}
12 \ivoagroup{http://www.ivoa.net/twiki/bin/view/IVOA/IvoaGridAndWebServices}
14 %\author[????URL????]{http://www.ivoa.net/twiki/bin/view/IVOA/IvoaGridAndWebServices}
15 \author{Brian Majour, Guy Rixon, Andr\`e Schaaff, Giuliano Taffoni}
17 \editor{Giuliano Taffoni}
19 \previousversion[http://www.ivoa.net/documents/cover/SSOAuthMech-20080124.html]{REC-1.0}
20 \previousversion[http://www.ivoa.net/documents/cover/SSOAuthMech-20070904.html]{PR-20070904}
21 \previousversion[http://www.ivoa.net/documents/cover/SSOAuthMech-20070621.html]{PR-20070621}
22 \previousversion[http://www.ivoa.net/documents/cover/SSOAuthMech-20060519.html]{WD-20060519}
25 \begin{document}
26 \begin{abstract}
27 Approved client-server authentication mechanisms are described for the IVOA single-sign-on profile: No Authentication; HTTP Basic Authentication; TLS with passwords; TLS with client certificates; Cookies; Open Authentication; Security Assertion Markup Language; OpenID. Normative rules are given for the implementation of these mechanisms, mainly by reference to pre-existing standards. The Authorization mechanisms are out of the scope of this document.
28 \end{abstract}
31 \section*{Acknowledgments}
33 This document derives from discussions among the Grid and Web Services working-group of IVOA. It is particularly informed by prototypes built by Matthew Graham (Caltech/US-NVO), Paul Harrison (ESO/EuroVO), David Morris (Cambridge/AstroGrid) and Raymond Plante (NCSA/US-NVO). The prior art for the use of proxy certificates comes from the Globus Alliance.
34 This document has been developed with support from the National Science Foundation's Information Technology Research Program under Cooperative Agreement AST0122449 with The Johns Hopkins University, from the UK Particle Physics and Astronomy Research Council (PPARC) and from the Europena Commission's Sixth Framework Program via the Optical Infrared Coordination Network (OPTICON).
37 \section*{Conformance-related definitions}
38 The words ``MUST'', ``SHALL'', ``SHOULD'', ``MAY'', ``RECOMMENDED'', and
39 ``OPTIONAL'' (in upper or lower case) used in this document are to be
40 interpreted as described in IETF standard, \citet{std:RFC2119}.
42 The \emph{Virtual Observatory (VO)} is
43 general term for a collection of federated resources that can be used
44 to conduct astronomical research, education, and outreach.
45 The \href{http://www.ivoa.net}{International
46 Virtual Observatory Alliance (IVOA)} is a global
47 collaboration of separately funded projects to develop standards and
48 infrastructure that enable VO applications.
51 \section{Introduction}
52 IVOA's single-sign-on architecture is a system in which users assign cryptographic credentials to user agents so that the agents may act with the user's identity and access rights. This standard describes how agents use those credentials to authenticate the user's identity in requests to services. This standard describes also the authentication mechanism of an application or a service making a call (on behalf of someone or something else) to an API or to another service.
53 This document is essentially a {\em profile} against existing security standards; that is, it describes how an existing standard should be applied in an IVOA application to support single sign-on capabilities in the IVOA. In the following sections, we make specific references to details spelled out in these standards. For the purposes of validating against this standard, those referenced documents should be consulted for a full explanation of those details. Unfortunately, a reader that is unfamiliar with these external standards might find this specification confusing. To alleviate this problem, each major section is concluded by a Commentary subsection that provides some explanations of the detailed terms and concepts being referred to. The Commentary subsection may also provide recommended scenarios for how this specification might actually be realised. Note that the statements in the Commentary subsections are non-normative and should not be considered part of precise specification; nevertheless, they are indicative of the intended spirit of this document.
55 \subsection{Role within the VO Architecture}
57 \begin{figure}
58 \centering
60 % Get the architecture diagram from the TCG chair
61 % http://wiki.ivoa.net/twiki/bin/view/IVOA/IvoaTCG
62 % If they give you a PDF, for now dumb it down to a png by
63 % convert -antialias -density 72x72 archdiag.pdf archdiag.png
64 % Oh -- Notes don't need this; you'd have to remove archdiag.png
65 % from FIGURES in the Makefile, too.
66 \includegraphics[width=0.9\textwidth]{SSO_image001.png}
67 \caption{Architecture diagram for this document}
68 \label{fig:archdiag}
69 \end{figure}
71 Fig.~\ref{fig:archdiag} shows the role this document plays within the
72 IVOA architecture \citep{note:VOARCH}.
75 \section{Scope of this standard}
76 \subsection{Requirements}
77 When a service is registered in an IVOA registry, that services resource document MAY include metadata expressing conformance to one or more of the authentication mechanisms approved in the IVOA SSO profile. Such a service MUST implement those mechanisms as described in this document, and clients of the service MUST participate in the mechanism when calling the service. Is a service does not provide any SSO specification it is assumed that no authentication is required.
78 The registration of the service interface SHALL contain an XML element
79 of type \xmlel{SecurityMethod} as specified in the XML schema for
80 VOResource \citep{std:VOR}. The value of this element distinguishes the
81 authentication mechanism using the values stated in the sections below.
82 Services registered without the metadata alluded to above need not
83 support any authentication mechanism. If they do require authentication,
84 they MAY use either the IVOA-standard mechanisms or others that are not
85 IVOA standards.
87 \subsection{Commentary}
88 The IVOA SSO profile allows the development of a ''realm'' of interoperable services and clients.
89 Service providers opt in to this realm by implementing this current standard and by registering accordingly in the IVOA registry.
90 This allows clients to discover a secured service through the registry and to be able to use it without
91 being customized for the details of the specific service.
93 Services within the Virtual Observatory that are not intended to be widely interoperable need not opt in to the SSO realm.
94 In particular, ''private'' services, accessed by web browsers and protected by passwords, are allowed.
95 However, these private services should be reworked to follow the IVOA standard if they are later promoted to a wider audience.
97 An example of a registration for a secured interface follows.
98 \begin{lstlisting}[language=XML]
99 <interface xmlns:vs='ivo://www.ivoa.net/xml/VODataService/v1.0'
100 xsi:type='vs:ParamHTTP'>
101 <accessURL>http://some.where/some/thing</accessURL>
102 <securityMethod>ivo://ivoa.net/sso#saml2.0</securityMethod>
103 </interface>
104 \end{lstlisting}
106 More than one {\xmlel securityMethod} can be specified:
107 \begin{lstlisting}[language=XML]
108 <interface xmlns:vs='ivo://www.ivoa.net/xml/VODataService/v1.0'
109 xsi:type='vs:ParamHTTP'>
110 <accessURL>http://some.where/some/thing</accessURL>
111 <securityMethod>ivo://ivoa.net/sso#saml2.0</securityMethod>
112 <securityMethod>ivo://ivoa.net/sso#cookie</securityMethod>
113 <securityMethod>ivo://ivoa.net/sso#OpenID</securityMethod>
114 </interface>
115 \end{lstlisting}
117 The order of the \xmlel{securityMethod} elements determines the priority of the method to use, in the example above the preferred method to access
118 the service is {\em SAML}, than {\em cookies} and finally if the other are not available OpenID.
120 \section{Approved authentication mechanisms}
122 The following authentication mechanisms are approved for use in the SSO profile.
123 \begin{itemize}
124 \item No authentication required.
125 \item HTTP Basic Authentication
126 \item Transport Layer Security (TLS) with passwords.
127 \item Transport Layer Security (TLS) with client certificates.
128 \item Cookies
129 \item Open Authentication (OAuth)
130 \item Security Assertion Markup Language (SAML)
131 \item OpenID
132 \end{itemize}
134 The mechanism is associated with the interface provided by the service and registered in the IVOA registry.
136 \begin{table}[th] \begin{tabular}{p{0.45\textwidth}p{0.64\textwidth}} \sptablerule
137 \textbf{SSO mechanism}&\textbf{\xmlel{<securityMethod>}}\\ \sptablerule
138 No authentication required & none\\
139 HTTP Basic Authentication &
140 \xmlel{https://www.w3.org/Protocols/HTTP/ 1.0/spec/html\#BasicAA}\\
141 TLS with password & \xmlel{ivo://ivoa.net/sso\#tls-with-password} \\
142 TLS with client certificate & \xmlel{ivo://ivoa.net/sso\#tls-with-certificate} \\
143 Cookies & \xmlel{ivo://ivoa.net/sso\#cookie} \\
144 Open Authentication & \xmlel{ivo://ivoa.net/sso\#OAuth} \\
145 SAML & \xmlel{ivo://ivoa.net/sso\#saml2.0} \\
146 OpenID & \xmlel{ivo://ivoa.net/sso\#OpenID} \\
147 \sptablerule
148 \caption{List of approved authentication mechanisms and the corresponding securityMethod}
149 \label{table:SMtable}
150 \end{tabular}
151 \end{table}
153 Services that are registered with a IVOA registry as having a {\em WebService} type interface
154 \citep{ivo:resource} SHALL support OAuth, or SHALL support cookies or SHALL support TLS with client
155 certificates or SHALL require no authentication.
156 Interfaces by which a user logs in to the SSO system SHALL support either
157 TLS with client certificates, or TLS with passwords, or SAML or a combination of them
159 \section{HTTP Basic Authentication}
160 \subsection{Requirements}
161 Services using HTTP basic authentication SHALL use the authentication mechanism described in the RFC7235 \citep{std:RFC7235}
162 that updates RFC2617 \citep{std:RFC2617}.
163 Interfaces using this mechanism SHALL be be registered with the security method
165 \texttt{https://www.w3.org/Protocols/HTTP/1.0/spec/html\#BasicAA}
167 \subsection{Commentary}
168 HTTP provides a simple challenge-response authentication framework that can be used by a server to challenge
169 a client request and by a client to provide authentication information.
170 The HTTP authentication framework does not define a single mechanism for maintaining the confidentiality of credentials.
171 HTTP depends on the security properties of the underlying transport- or session-level connection to provide
172 confidential transmission of header fields. Connection secured with TLS are recommended prior to exchanging any credentials.
174 \section{Details of TLS}
175 \subsection{Requirements}
176 Services using Transport Layer Security (TLS) SHALL do so according to the TLS v1.2 standard RFC5246 \citep{std:RFC5246}.
178 \subsection{Commentary}
179 TLS supersedes the Secure Sockets Layer that is an outdated cryptographic protocol.
180 TLS v1.0 was based on SSL v3.0; the current version of TLS is V1.2 described in by \citet{std:RFC5246}.
181 TLS v1.2 is backwards compatible with TLS v1.0, TLS v1.1 and SSL v3.0.
182 ``TLS versions 1.0, 1.1, and 1.2, and SSL 3.0 are very similar, and use compatible ClientHello messages;
183 thus, supporting all of them is relatively easy.[...] TLS 1.2 clients that wish to support SSL 2.0 servers MUST
184 send version 2.0 CLIENT-HELLO messages defined in SSL2.'' \citep{std:RFC5246}.
186 \section{Details of TLS-with-client-certificate}
187 \subsection{Requirements}
188 Certificates SHALL be transmitted and checked according to the TLS v1.2 standard RFC5246.
190 Services implementing TLS MUST support certificate chains including proxy certificates according to RFC6818 \citep{std:RFC6818}.
192 Interfaces using this mechanism SHALL be be registered with the security method
194 \texttt{ivo://ivoa.net/sso\#tls-with-certificate}.
196 \subsection{Commentary}
197 When Mutual Certificate Authentication is configured for REST services, both, the client and the service perform
198 identity verification or authentication through X.509 certificates.
200 The client authenticates the service during the initial SSL handshake, when the server sends the client a certificate to authenticate itself.
202 \section{Details of TLS-with-password}
203 \subsection{Requirements}
204 The user-name and password SHALL be passed in the message protected by the TLS mechanism,
205 not as part of the mechanism itself. The ``HTTP basic authentication'' should be used with particular attention.
207 Interfaces using this mechanism SHALL be be registered with the security method
209 \texttt{ivo://ivoa.net/sso\#tls-with-password}.
211 \subsection{Commentary}
212 ``HTTP basic authentication'' passes the user-name and password in the HTTP headers,
213 assuming that the credentials are not a natural part of the message body.
214 This standard applies the TLS-with-Password mechanism only to the special case of logging in to the SSO realm.
215 Hence, the user name and password are logically part of the message body, not the message header.
217 \section{The use of Cookies}
218 \subsection{Requirements}
219 Cookie-Based Authentication uses server side cookies to authenticate the user on every request.
220 The way to manage cookies for authentication is described in RFC6265 \citep{std:RFC6265}.
222 Interfaces using this mechanism SHALL be be registered with the security method
224 \texttt{ivo://ivoa.net/sso\#cookie}.
227 \subsection{Commentary}
228 RESTful web services should use session-based authentication, either by establishing a session token via a POST or
229 by using an API key as a POST body argument or as a cookie.
230 User names, passwords, session tokens, and API keys should not appear in the URL,
231 as this can be captured in web server logs, which makes them intrinsically valuable.
232 \begin{figure}
233 \centering
234 \includegraphics[width=0.9\textwidth]{SSO_image002.png}
235 \caption{Simplified picture of SAML 2.0 authentication.}
236 \label{fig:saml}
237 \end{figure}
239 \section{Details on SAML authentication}
240 \subsection{Requirements}
241 Services using SAML authentication mechanisms SHALL do so according to the
242 saml-core-2.0-os OASIS standard \citep{std:SAML}.
243 SAML includes protocols and protocol bindings and security \citep{std:SAMLB}.
245 Interfaces using this mechanism SHALL be be registered with the security method
247 \texttt{ivo://ivoa.net/sso\#saml2.0}.
250 \subsection{Commentary}
251 SAML presumes two primary roles in any transaction: the organisation where the identity is established,
252 known as the Identity Provider (``IdP''), or Asserting Party (``AP'');
253 and the organisation which (for this transaction) wants to use this identity, known as the Service Provider (``SP''),
254 or Relying Party (``RP'').
256 A user attempts to access an application with the Service Provider.
257 The SP needs to establish the identity of this user, and so sends an authentication request to the Identity Provider.
259 The user authenticate with the IdP (IdP is taking care of the authentication mechanisms and protocols e.g. Kerberos, ldap etc.) so the IdP can send back an `Assertion' to the SP.
260 Now the SP knows who the user is, and can process that user accordingly (see Fig.~\ref{fig:saml}).
261 \begin{figure}
262 \centering
263 \includegraphics[width=0.9\textwidth]{SSO_image003.png}
264 \caption{Simplified picture of OAuth 2.0 authentication.}
265 \label{fig:oauth}
266 \end{figure}
268 SAML2.0 protocol allows also to implement authentication service discovery mechanisms. SAML2.0 defines a browser-based protocol
269 by which a centralized discovery service can provide a requesting service provider with the unique identifier of an
270 identity provider that can authenticate a principal. In this way
273 \section{Details on OAuth}
274 \subsection{Requirements}
275 Services using OAuth authentication mechanisms SHALL do so according to the RFC6749 \citep{std:RFC6742}.
277 Interfaces using this mechanism SHALL be be registered with the security method
279 \texttt{ivo://ivoa.net/sso\#OAuth}.
282 \subsection{Commentary}
283 Open Authentication 2.0 (also in conjunction with OpenID Connect) is actually the adopted standard
284 to handle identity in the framework of RESTful web services.
285 OAuth is used when an application is making a request on behalf of a user.
287 OAuth introduces the notion of an `authorization token', a `refresh token' and Authorization Service (AS).
288 The `authorization' token states that the client application has the right to access services on the server (see Fig.~\ref{fig:oauth}).
289 However, it does not supersede any access control decisions that the server-side application might make.
291 OAuth is related to delegate credential from an application to another.
293 \section{Details on OpenID}
294 \subsection{Requirements}
295 Services using OpenID authentication mechanisms SHALL do so according to the OpenID Foundation standards \citep{std:openid}
297 Interfaces using this mechanism SHALL be be registered with the security method
299 \texttt{ivo://ivoa.net/sso\#OpenID}.
302 \subsection{Commentary}
303 OpenID is an open and decentralized authentication and identity system. OpenID relying parties do not manage end user credentials
304 such as passwords or any other sensitive information which makes authentication and identity management much simpler and secure.
305 In a RESTful environment OpenID Connect \citep{std:openidconnect} is commonly adopted as authentication solution. ``OpenID Connect is a simple identity
306 layer on top of the OAuth 2.0 protocol, which allows computing clients to verify the identity of an end-user based on the authentication
307 performed by an authorization server, as well as to obtain basic profile information about the end-user in an interoperable and REST-like manner.'' \citep{std:openid}.
309 \appendix
310 \section{VOResource SecurityMethod}
311 This Appendix presents an extract of the VOResource Description XML schema.
312 Here we present the part of the schema regarding the \xmlel{SecurityMethod} element
313 to facilitate the reader identify the relevant schema sections in the VOResource Description.
316 \begin{lstlisting}[language=xml,basicstyle=\footnotesize]
317 <xs:schema xmlns="http://www.w3.org/2001/XMLSchema"
318 xmlns:xs="http://www.w3.org/2001/XMLSchema"
319 xmlns:vr="http://www.ivoa.net/xml/VOResource/v1.0"
320 xmlns:vm="http://www.ivoa.net/xml/VOMetadata/v0.1"
321 targetNamespace="http://www.ivoa.net/xml/VOResource/v1.0"
322 elementFormDefault="unqualified" attributeFormDefault="unqualified" version="1.02">
323 <xs:annotation>...</xs:annotation>
324 <xs:simpleType name="UTCTimestamp">...</xs:simpleType>
325 <xs:simpleType name="UTCDateTime">...</xs:simpleType>
326 <xs:complexType name="Resource">...</xs:complexType>
327 <xs:simpleType name="ValidationLevel">...</xs:simpleType>
328 <xs:complexType name="Validation">...</xs:complexType>
329 <xs:simpleType name="AuthorityID">...</xs:simpleType>
330 <xs:simpleType name="ResourceKey">...</xs:simpleType>
331 <xs:simpleType name="IdentifierURI">...</xs:simpleType>
332 <xs:simpleType name="ShortName">...</xs:simpleType>
333 <xs:complexType name="Curation">...</xs:complexType>
334 <xs:complexType name="ResourceName">...</xs:complexType>
335 <xs:complexType name="Contact">...</xs:complexType>
336 <xs:complexType name="Creator">...</xs:complexType>
337 <xs:complexType name="Date">...</xs:complexType>
338 <xs:complexType name="Content">...</xs:complexType>
339 <xs:complexType name="Source">...</xs:complexType>
340 <xs:simpleType name="Type">...</xs:simpleType>
341 <xs:simpleType name="ContentLevel">...</xs:simpleType>
342 <xs:complexType name="Relationship">...</xs:complexType>
343 <xs:complexType name="Organisation">...</xs:complexType>
344 <xs:complexType name="Service">...</xs:complexType>
345 <xs:simpleType name="Rights">...</xs:simpleType>
346 <xs:complexType name="Capability">...</xs:complexType>
347 <xs:complexType name="Interface" abstract="true">
348 <xs:annotation>...</xs:annotation>
349 <xs:sequence>
350 <xs:element name="accessURL" type="vr:AccessURL"
351 minOccurs="1" maxOccurs="unbounded">...</xs:element>
352 <xs:element name="securityMethod" type="vr:SecurityMethod"
353 minOccurs="0" maxOccurs="unbounded">
354 <xs:annotation>
355 <xs:documentation> the mechanism the client must employ to
356 gain secure access to the service.
357 </xs:documentation>
358 <xs:documentation> when more than one method is listed, each one
359 must be employed to gain access.
360 </xs:documentation>
361 </xs:annotation>
362 </xs:element>
363 </xs:sequence>
364 <xs:attribute name="version" type="xs:string" default="1.0">...</xs:attribute>
365 <xs:attribute name="role" type="xs:NMTOKEN">...</xs:attribute>
366 </xs:complexType>
367 <xs:complexType name="AccessURL">...</xs:complexType>
368 <xs:complexType name="SecurityMethod">
369 <xs:annotation>
370 <xs:documentation>a description of a security mechanism.</xs:documentation>
371 <xs:documentation> this type only allows one to refer to the mechanism via a URI.
372 Derived types would allow for more metadata.
373 </xs:documentation>
374 </xs:annotation>
375 <xs:sequence/>
376 <xs:attribute name="standardID" type="xs:anyURI">
377 <xs:annotation>
378 <xs:documentation> A URI identifier for a standard security mechanism. </xs:documentation>
379 <xs:documentation>
380 This provides a unique way to refer to a security specification standard.
381 The use of an IVOA identifier here implies that a VOResource
382 description of the standard is registered and accessible.
383 </xs:documentation>
384 </xs:annotation>
385 </xs:attribute>
386 </xs:complexType>
387 <xs:complexType name="WebBrowser">...</xs:complexType>
388 <xs:complexType name="WebService">...</xs:complexType>
389 </xs:schema>
390 \end{lstlisting}
393 \section{Changes from Previous Versions}
396 \subsection {Changes from v. 1.01}
397 \begin{itemize}
398 \item We remove all the references to SOAP as deprecated from IVOA
399 \item We add new security methods ad relative discussion sessions: OpenID, SAML, Cookies, HTTP basic authentication
400 \end{itemize}
403 \bibliography{ivoatex/ivoabib,SSOAuthMech}
406 \end{document}

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