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1 \chapter{Grid computing \& Security}
2 % Authenticatie is gebaseerd op PKI
3 % Authorisatie is gebaseerd op DN's, VOMS
4 % Grid heeft dit en dat, maar onze basis is PKI.
5 % Authenticatie: persoonlijke certificaten, VOMS, SAML statements en
6 \section{Authentication \& authorization mechanisms}
7 Grid computing requires a mechanism to authorize users' access to Grid resources.
8 This authorization can be granted at different levels depending on different types of credentials supplied by - or associated with - the user and on which service he or she tries to access.
9
10 \subsection{X.509 certificates}
11 The various Grid middleware stacks rely heavily on X.509 certificates \cite{rfc2459} as the 'lingua Franca' for authenticating users.
12 It's a personal public key certificate that can be traced back to the issuer, a \textit{Certificate Authority} (CA).
13
14 It contains (among other things):
15 \begin{itemize}
16 \item The subject \textit{Distinguished Name} (DN), which identifies the person, service or system that the certificate represents
17 \item The subject's public key
18 \item The identity of a CA that has signed the certificate, attesting to the authenticity of the subject DN and public key
19 \item The digital signature of the named CA
20 \end{itemize}
21
22 \glossary{name={CA}, description={Certificate Authority}}
23 \glossary{name={DN}, description={Distinguished Name}}
24 \glossary{name={GSI}, description={Grid Security Infrastructure}}
25 \glossary{name={SSO}, description={Single sign-on}}
26 \glossary{name={PKI}, description={Public Key Infrastructure}}
27
28 This creates a \textit{Public Key Infrastructure} (PKI) \cite{rfc3280} wherein the CA is trusted and can give users, systems and services access to Grid resources.
29 The \textit{Grid Security Infrastructure} (GSI) is a specification to support security between organisation boundaries, allow secure communication and enable "single sign-on" (SSO) solutions in Grid computing.
30 It can be used to enable a SSO solution through delegation of X.509 certificates.
31
32 The certificates used on Grid systems are \textit{Proxy Certificates} \cite{rfc3820} which are signed by the subject and are valid for shorter periods of time to diminish the value of stolen proxy certificates.
33 These proxy certificates can be traced back to the user they belong to, providing end-to-end accountability.
34
35 % TODO ref GSI
36
37 % SSO, delegation -> trace
38
39 % VOMS doet registratie van gebruikers op basis van hun DN, groepsstructuur en rollen toekennen
40 % Signed attribute certificates uit te geven.
41 % FQANS zijn onderdeel van de VOMS attributes.
42 \subsection{Virtual Organizations}
43 \label{vo_section}
44 Because of scalability issues, Grid authentication is mostly based on group affiliation.
45 The group affiliations are expressed in several tiers, the most high level of which is a \textit{Virtual Organization} (VO).
46 \glossary{name={VO}, description={Virtual Organization}}
47 VOs appear to work like regular organizations, but are not explicitly connected by location, employer or other affiliation.
48 However they collaborate and present themselves as a unified organization, working towards a common goal.
49
50 \subsubsection{Virtual Organization Management Service}
51 VOs can make use of a \textit{Virtual Organization Management Service} (VOMS) to manage and register their users.
52 \glossary{name={VOMS}, description={Virtual Organization Management Service}}
53 Users should apply to a VOMS with their Grid certificate, which must contain the name of the user in the certificate's Subject \textit{Distinguished Name} (DN).
54
55 Based on a user's Grid certificate credentials - specifically, the Subject DN - the VOMS service can give a user signed tokens to claim group membership when interacting with Grid services.
56 In this interaction the VOMS server acts as an \textit{Attribute Authority} (AA), which distributes signed attributes to the user in the form of an \textit{Attribute Certificate} (AC) \cite{rfc3281}.
57 The Attribute Certificate also specifies the group, subgroup, roles and capabilities of the holder.
58 \glossary{name={AA}, description={Attribute Authority}}
59 \glossary{name={AC}, description={Attribute Certificate}}
60 To create a VOMS AC, a VOMS service amends the user's proxy certificate with signed VOMS tokens, which include \textit{Fully Qualified Attribute Name}s (FQANs) \cite{fqan}.
61 \glossary{name={FQAN}, description={Fully Qualified Attribute Name}}
62
63 As an analogy, in this capacity the Grid certificate is like a passport that is used to obtain a membership card (AC) of a certain club (VO).
64 Once the identity of the holder has been verified, the membership card is all that is needed to access club facilities. Their identity can be established from these \textit{attribute credentials}.
65
66 A user can be authenticated to belong to a VO group by tracing this information back to a trusted VOMS server certificate (an \textit{Attribute Signing Certificate} \cite{rfc3281}), which has in turn been signed by a trusted CA.
67 Based on these signed attributes a user is authenticated to belong to a project group in a certain role.
68 This authentication solution requires the trusted VOMS server certificates to be available to all services that need to verify VOMS attributes.
69
70 %VOMS defines groups, roles and capabilities.
71 %These are completely independent of each other.
72 %Roles are meant to be global, associated directly with the AC holder, regardless of group membership.
73 %However, VOMS allows groups and roles to be bound together, using one as a qualifier for the other.
74 %While it is indeed possible to encode groups and roles inside the standard attributes in a format that could represent
75 %this information, there is no way to have the same format also be readable by other AC users without risking misunderstandings. \cite{ac-rfc}
76
77 \subsection{Pool accounts}
78 \label{poolaccounts_section}
79 Pool accounts are part of a mechanism to map users' Grid certificate credentials to actual Unix user accounts on compute clusters. \cite{gridmapdirsite}
80 These pool accounts are generic user accounts that are mapped to the remote user based on the credentials in their certificate.
81 The various sets of pool accounts are created by site administrators, which are then 'leased' to users working in certain roles.
82 The pool accounts are not associated with a user in their initial setup.
83
84 When a pool account is in use, there is a strong link between the pool account and the user credentials that were mapped to it.
85
86 A pool account is a regular Unix account that is already present on a system and is already setup to have certain particular privileges of a particular group of users that might also have a specific role e.g. a Production manager, Software Manager or regular user.
87 In its initial state a pool account is not associated to any user.
88 During the mapping process a user's credentials are mapped to a specific pool account which means that the selected free pool account is strongly tied to the set of user credentials.
89
90 % pool accounts zijn niet geassocieerd met gebruiker totdat die is langsgekomen/gemapped
91 % gebruikers zijn op deze manier sterk verbonden met het UNIX account
92 %This facilitates late binding between users within a VO and the concrete UNIX accounts they use to do work on the Grid.
93 The role and associated capabilities a user takes on are determined by the signed VOMS attributes present in a user's proxy certificate. \cite{nikhefwebsite:gridwikiindex}
94
95 System administrators can disassociate pool accounts after a certain period of time, mostly due to inactivity of the user in the order of several weeks or months (depending on the site local policies).
96 The unassociated accounts are returned to the pool for reuse.
97
98
99 \subsection{Fully Qualified Attribute Names}
100 \label{fqan_section}
101 \textit{Fully Qualified Attribute Names} (FQANs) are explicit and unambiguous strings that can describe the group and subgroups a user is associated with.
102 These can be given out by a VOMS service through an Attribute Certificate.
103 Besides group affiliation, roles and capabilities can be attributed to the user.
104 By being affiliated with a certain group, a user can claim authorization at a grid service.
105
106 It is up to a service to take a local policy and the presented credentials into account, base authorization on them and allow a certain action.
107 The result can be different for every site and service type.
108
109 Please see table \ref{fqan_table} for an example of the information that can be expressed in an FQAN string.
110
111 %In VOMS AC's komen FQANS voor
112 %FQAN is 1 string die beschrijving geeft van de VO groepen, subgroepen, rollen en capabilities
113 % binnen iedere groep kun je aparte rollen aanwijzen
114 % als je die rollen bezit mag je de authorizatie claimen bij een service
115 % mag meer tekst bij
116
117 \begin{table}[h]
118 \begin{center}
119 \begin{tabular}{ | c | c | c | c | }
120 \hline
121 VO & group & subgroup & role \\
122 \hline
123 /fred.example.org & /production & /optimization & /Role=Admin \\
124 \hline
125 \end{tabular}
126 \end{center}
127 \caption[FQAN fields]{A table showing examples of the FQAN fields VO, group, subgroup and role}
128 \label{fqan_table}
129 \end{table}
130
131 % Mensen moeten zich via email aanmelden bij de VOMS-server
132 % Alle grid services en VOMS servers hebben een push-model waarin je je certificate upload. De services moeten deze informatie verifieren.
133
134 %All Grid services have a push model that requires users to provide a certificate which is then verified by the service. This is done by tracing back the proxy certificate and all its signed credentials to the VOMS server certificate, and tracing the user certificate back to the issuing CA.
135
136 \subsection{Grid credentials}
137 % Basis van de authenticatie is gebaseerd op de persoonlijke certificaten.
138 % Die zijn uitbreidbaar.
139 %
140
141 Multiple authentication mechanisms must be supported due to the scale and breadth of the Grid use cases.
142 Many different organizations worldwide develop Grid middleware, policies and infrastructure and each organization brings their own use cases, motivations and expertise to the table.
143 %breed -> veel verschillende groepen schrijven middleware en hebben ieder hun eigen use-cases te verwerken daarin EN diverse achtergronden en motivaties
144 % Bepaalde technieken, evolutie ervan, adoptie/penetratie van technieken die we hebben.
145 % Open standaarden die we zoveel mogelijk willen ondersteunen.
146 % SAML is heel nieuw, PKI bestaat al heel lang, en daarbij: proxy delegations.
147 % Door Delegation of credentials from your certificate to a WMS zodat die service functioneert als een agent.
148 % Alleen de private key van de delegation blijft over op de WMS. Je eigen private key van je op jouw naam staande certificate wordt niet overdragen aan de agent.
149 % Het proxy certificate is cryptografisch verbonden, omdat jij de signer bent.
150 %Support for these mechanisms has evolved over the past decade, and gradually got more flexible.
151 Interoperability standards for various middleware stacks have evolved over the past decade, and have led to more flexible middleware services.
152 % Het gebruik van de authenticatie technieken heeft relatie tot volwassenheid en evolutie van authenticatie technieken en de use cases (refereer naar delegation). Open standaarden zijn vereist.
153
154 % End-to-end security: dat je de chain van de worker node kunt terugleiden naar de persoon die de job submitte.
155 % Vanwege de schaalbaarheid maken we vooral authorisatie beslissingen op basis van groepen.
156 % Mensen die in die groep zitten worden impliciet vertrouwd.
157 % VOMS: Virtual Organization staat min of meer 1:1 tot een experiment of een project.
158 % Binnen de VO kennen we groepen, subgroepen en rollen. Aan ieder van deze kunnen personen worden toegewezen, en ook services en resources.
159 % Individu moet zich registeren bij een VO, en als je geregistreerd bent kun je gesignede tokens ophalen.
160 % User genereert een certificate en laat hem signen door een CA.
161 % User kan een proxy certificate maken van z'n user cert.
162 % Daarmee authenticeer je jezelfd bij de VOMS server (standaard mutual SSL authentication) en vraag je de groepen van jouw VO en evt. rollen.
163 % De server zoekt die credentials bij elkaar en signed ze met zijn private key. Vervolgens stuurt ie de gesignede blob (VOMS attribute Certificate of VOMS AC) terug naar de client.
164 % Nu ga je een nieuwe proxy delegation maken, en tijdens het signing request worden de VOMS AC embedded in de CSR als X.509v3 extensies.
165 % Dit geheel wordt nu gesigned als een reguliere met jouw eigen private key.
166
167 % VOMS AC's zijn gebaseerd op RFC 3281.
168 % Certificates waren gebaseerd op RFC 3280, maar nu is dat RFC 5280
169
170 % Nu heb je een VOMS-enabled certificate (VOMS proxy).
171 % Attributes in een VOMS proxy zijn:
172 % Van de VOMS server die signed: de URI, de DN, de signer van de DN.
173 % Dus je hebt twee dingen om te controleren: de cert van de VOMS (naar de CA) en de signer (ook CA) van de DN.
174
175 % IGTF is een samenwerking van 3 grote grid (igtf.net)
176 % PKI + personal certificates.
177 % Binnen de rest van VOMS certificate attributes heb je ook FQANS die vertellen welke groep en/of rol voor jou van toepassing is. Wordt ook gesigned door de VOMS service.
178 % (Dan heb je ook nog een name-value pair voor mogelijk extra attributen.)
179
180
181 % Nog 2 dingen die in je VOMS proxy kunnen zitten:
182 % Public key van de voms service.
183 % Serial number van jouw persoonlijke certificaat.
184 % Jouw subject DN.
185
186
187 % Zo is er een linkt te leggen tussen:
188 % Jouw subject DN, jouw CA, en jouw serial number van jouw certificaat.
189 % Zo ontstaat er een link tussen de persoon, de signature van de CA en het certificaat van de gebruiker. Dit gaat het stelen van voms-attributes tegen want voms attributes zitten als extensie in je proxy certificaat en dus hebben ze een sterke binding nodig met de eigenaar van het certificaat.
190
191 % VOMS AC
192 % DN, FQAN, CA, serial number, secret sauce.
193 Different types of credentials that can be used are:
194 \begin{description}
195 \item[Personal, host and service X.509 certificates] % Wie ben je
196 % TODO personal might also be for a robot/agent
197 {The Subject \textit{Distinguished Name} (DN) is a field in an X.509 certificate.
198 It's composed of multiple \textit{Relative Distinguished Name}s (RDN) \cite{rfc2253} \cite{rfc2511}.
199 This uniquely identifies a user, host or service through a PKI infrastructure which includes identity-vetting by a trusted third party.
200
201 The subject DN is mostly used in the OpenSSL oneline format \cite{how_to_handle_openssl}.
202 Another supported format that is less used is the X.500 \cite{rfc2253} notation of the DN.
203
204 }
205
206 \item[VOMS attributes]{
207 The DN information is used to query a certain VOMS server associated with a project, which returns an \textit{Attribute Certificate} \cite{rfc3281} in which each field and the Attribute Certificate as a whole are signed by the VOMS server.
208 This mechanism is explained in more detail in section \ref{vo_section}.
209 }
210
211 % Op basis van de info in het certificaat (je DN) en VOMS credentials (FQAN) worden user geauthoriseerd.
212 % (Wie ben je, voor welke groep werk je, wat is je rol).
213
214 %\item VOMS credentials (Fully Qualified Attribute Name) % Voor welke groep werk je en welke rol bekleed je
215 % Voorbeelden van VOMS rollen: VO-admins, software updaters / installateurs (Software area directories), production managers (verantwoordelijke voor het processen van de data en monte carlo productie).
216 \item[SAML statements] % Zie je terug in Shibolleth. Altijd terug te leiden naar X.509 certificates. Andere niet-standaard authenticatiemethoden. Komt meer uit de web-hoek.
217
218 {The \textit{Security Assessment Markup Language} \cite{saml} is an XML standard for exchanging authentication and authorization data between security domains.
219 Grid services will attempt to translate SAML information back to an X.509 certificate, as it remains the 'lingua Franca' for communicating credentials.
220 }
221 \glossary{name={SAML}, description={Security Assessment Markup Language}}
222 % Bedoeld om een claim te geven over identiteit
223 % These statements lead users back to a X.509 certificate.
224 % The standard was devised for interoperability between Single Sign-on solutions.}
225 % reference SSO
226 % reference SAML
227
228 \item[XACML queries] % Te maken met policies en queries op policies. Mag pietje puk gebruik maken van deze resource? XACML: Subject (aram + cert), Action (computing), Resource (storage), Environment (arbitraire omgevingsinformatie).
229
230 {The \textit{eXtensible Access Control Markup Language} (XACML) \cite{xacml} is a declarative access control policy language implemented in XML.
231 XACML is very expressive and therefore useful to create and evaluate complex authorization policies.
232 It can be used to define rules based on Subject, Action, Resource, and Environment values.
233 Please see table \ref{xacml_table} for an example of the information that can be used to create ACL policies in XACML.
234 %\subsection{XACML fields}
235 \glossary{name={XACML}, description={eXtensible Access Control Markup Language}}
236
237
238 }
239 % reference XACML
240
241 \end{description}
242
243 \begin{table}[h]
244 \begin{center}
245 \begin{tabular}{ | c | c | c | c | }
246 \hline
247 Subject & Action & Resource & Environment \\
248 \hline
249 User Aram & needs cycles & on this server & which should run Linux \\
250 \hline
251 \end{tabular}
252 \end{center}
253 \caption[XACML concepts]{A table showing examples of the XACML concepts Subject, Action, Resource, and Environment}
254 \label{xacml_table}
255 \end{table}
256
257
258 %\section{XACML examples}
259 %Here's an example of how XACML requests can are used to represent Grid credentials.
260 %\subsection{Subject X.509 id}
261 %\begin{verbatim}
262 %<Attribute
263 %AttributeId="http://authz-interop.org/xacml/subject/subject-x509-id"
264 %DataType="http://www.w3.org/2001/XMLSchema#string">
265 %<AttributeValue>
266 %/O=dutchgrid/O=users/O=nikhef/CN=Oscar Koeroo
267 %</AttributeValue>
268 %</Attribute>
269 %\end{verbatim}
270
271 %\subsection{Subject X.500 issuer}
272 %\begin{verbatim}
273 %<Attribute
274 %AttributeId="http://authz-interop.org/xacml/subject/subject-x509-issuer"
275 %DataType="http://www.w3.org/2001/XMLSchema#string">
276 %<AttributeValue>
277 %/C=NL/O=NIKHEF/CN=NIKHEF medium-security certification auth
278 %</AttributeValue>
279 %</Attribute>
280 %\end{verbatim}
281
282
283 %\subsection{Subject VO}
284 %\begin{verbatim}
285 %<Attribute
286 %AttributeId="http://authz-interop.org/xacml/subject/vo"
287 %DataType="http://www.w3.org/2001/XMLSchema#string">
288 %<AttributeValue>gin.ggf.org</AttributeValue>
289 %</Attribute>
290 %\end{verbatim}
291
292
293 % PEPd -> Policy Enforcement Point daemon
294 % PDP -> Policy Decision Point
295 % PAP -> Policy Administration Point
296 % END USE CASES
297
298 \pagebreak
299
300 \section{Grid security middleware and services in gLite}
301 %TODO? vragen of dit SAC in de titel moet hebben
302 %\subsection{ADAM}
303 %% No longer used.
304 %ADAM stands for \textit{AmPS Data Analysis Method}, which as the name implies was first developed to process data generated by the AmPS \textit{Amsterdam Pulse Stretcher}.
305 %\glossary{name={ADAM}, description={AmPS Data Analysis Method}}
306 %\glossary{name={AmPS}, description={Amsterdam Pulse Stretcher}}
307 %It was not designed as a security middleware, but it does have a pluggable architecture to extend its functionality.
308 %The core component was a framework that got raw data as input from the detectors and used specific plug-ins to perform detector specific analysis. \cite{adampage}
309
310 This chapter tries to give a brief overview of the \textit{Site Access Control} (SAC) suite in the gLite middleware stack.
311 The SAC suite, comprising LCAS, LCMAPS, SCAS and gLExec, provides the mechanisms to implement authorization decisions and to make (and enforce) a mapping from grid credentials to the Unix world.
312 %Please see appendix \ref{use_cases} for a schematic describing the different systems interacting at a Grid site.
313
314 For an introduction to the gLite middleware stack please see the \textit{gLite user guide} \cite{glite_user_guide}.
315 For a reference to the SAC suite please refer to the \textit{Nikhef GridWiki} \cite{nikhefwebsite:gridwikisac}.
316 Please see appendix \ref{use_cases} for a description of possible use cases and the roles of the systems involved.
317
318 \subsection{gLExec}
319 %By the virtue of the pilot job framework use case a Worker Node has now become a new entry point to the cluster.
320 % reference naar suEXEC
321 gLExec is a pluggable suEXEC-like \cite{suexec} wrapper program that requests a mapping between Grid credentials and Unix user accounts and groups.
322 It can enforce this mapping to wrapped executables by modifying the \textit{uid} and \textit{gid}s of the executing process to the ones the user is mapped to, before passing execution to the wrapped binary.
323 gLExec will authenticate credentials using a callout to LCAS and LCMAPS, which provide authorization and user mapping facilities respectively.
324 %It can act as both a light-weight 'gatekeeper' on the Compute Element or be used on the Worker Node for late-binding (pilot job) use cases.
325 The callout to LCMAPS can procure a pool account by itself, but also through the SCAS client in LCMAPS.
326
327 \subsection{LCAS}
328 The \textit{Local Centre Authorization Service} (LCAS) makes binary ('yes or no') authorization decisions at the site and resource level.
329 \glossary{name={LCAS}, description={Local Centre Authorization Service}}
330 %In making this decision it can use a variety of inputs, among which are:
331
332 %\begin{itemize}
333 %\item The 'Grid' name of the user. The user's X.509 certificate Subject, also known as the \textit{Distinguished Name} (DN)
334 %\item Any VO attributes the user has like VOMS \cite{vomssite} \textit{Fully Qualified Attribute Name}s (FQANs)
335 %\item The name of the executable the user intends to execute
336 %\end{itemize}
337
338 It supports basic black and white list functionality, but also more complex VOMS-based expressions, based on the GACL \cite{gaclsite:home} language.
339 The framework fetches data, stores it, and offers structures to plug-ins that contain the following values:
340
341 \begin{itemize}
342 \item X.509 certificate chain string (in PEM \cite{rfc1421} format) \cite{rfc2459}
343 \item \textit{Resource Specification Language} (RSL) string \cite{globus-rsl}
344 \item \textit{Distinguished Name} (DN) string \cite{rfc5280}
345 \item Globus GSS Credential structure \cite{rfc2743}
346 \end{itemize}
347 \glossary{name={RSL}, description={Resource Specification Language}}
348 \glossary{name={PEM}, description={Privacy Enhanced Mail}}
349 \glossary{name={GACL}, description={Grid Access Control Library}}
350
351 \subsubsection{Plug-ins}
352 Site admins can configure plug-ins to enforce their authorization policy.
353 The plug-ins that LCAS executes must all exit successfully before authorization can continue. \cite{nikhefwebsite:gridwikiindex}
354 Here are the plug-ins \cite{lcas_apidoc} available at the time of writing.
355
356 \begin{description}
357 %\item[Gridlist]{A plug-in that maps allowed users to pool accounts using the gridmapfile \cite{gridmapfile}}
358 \item[Timeslots]{A plug-in that makes authorization decisions based on the time of day a job request is received.}
359 \item[Userban]{A plug-in that checks a file that contains a list of Subject DNs of users to be banned from the site.}
360 \item[Userallow]{A plug-in that checks a file that contains a list of Subject DNs of users to be allowed to the site.}
361 \item[Check executable]{A plug-in that checks if the executable requested is whitelisted by the service.}
362 \item[VOMS]{Works like the userallow plug-in, except it verifies the FQANs present in a proxy certificate instead of the Subject DN.
363 (Please see section \ref{fqan_section} for an explanation of FQAN attributes.)
364
365 These were added to the certificate by a VOMS service. With this plug-in, more complex policies for authorization can also be expressed in the GACL \cite{gaclsite:home} language.}
366 \end{description}
367
368 \glossary{name={RSL}, description={Resource Specification Language}}
369 \glossary{name={GACL}, description={Grid Access Control Library}}
370 % i.e. the plug-ins must be true if logically AND-ed.
371
372 \subsection{LCMAPS}
373 %Unix (like) systems only understand Unix UID, GID and Secondary GID
374 %credentials. As the lingua Franca is X.509 (with VOMS credentials), these
375 %credentials will need to be translated to Unix credentials.
376 %Based on the Unix credentials, batch system schedulers can do their work as
377 %batch systems have never (yet) been Griddified to natively handle X.509
378 %and/or VOMS credentials.
379
380 LCMAPS is the \textit{Local Credential Mapping Service}.
381 \glossary{name={LCMAPS}, description={Local Credential Mapping Service}}
382 It takes care of translating Grid credentials to Unix credentials local to a Grid site.
383 LCMAPS can ensure that, within a site, different individuals on the Grid maintain distinct, isolated Unix user accounts using the pool account mechanism \cite{gridmapdirsite}.
384 Please see section \ref{poolaccounts_section} for a description of the pool account mechanism.
385
386 A set of user credentials, i.e. the Subject DN or associated group and role affiliations listed in the VOMS attributes, will be linked to a specific pool account.
387 When a user returns to the same site with the same set of credentials the user will be mapped to the same Unix account again.
388
389 This mechanism can be extended to dynamic groups when needed.
390 LCMAPS can also interact with a site-local LDAP database to translate Grid credentials into site-local credentials.
391 Using group mappings based on the user's VO attributes, scheduling priority decisions can be made.
392 %TODO? ... in the LRMS?
393
394 The LCMAPS framework hosts a list of specific credential types in its core.
395 These are offered to the plug-ins via an API.
396 Each plug-in has a specific task to perform like in the LCAS framework.
397 These plug-ins can be used to configure policies for site-local access by Grid-wide users.
398 The plug-ins are able to write intermediate or final results into a part of the internal memory of the framework.
399
400 % BEGIN oscar
401 \label{lcmaps_failover}
402 The LCMAPS framework has two failover mechanisms in the execution of its loaded plug-ins that can be defined by the configuration file.
403 The first failover mechanism is similar to a state machine.
404 If a plug-in 'a' executes and its execution was a success, then progress to plug-in 'b'.
405 Otherwise progress to plug-in 'c'.
406 The state machine must end with a successful result.
407
408 The second failover mechanism is to define (execution) policies.
409 Each complete state machine is an authorization policy.
410 If multiple policies are defined and if the calling application allows it, then on a failure of such policy the framework can select the next policy to execute.
411 Between policy switch the internal memory (which holds the intermediate results) will be erased. \cite{nikhefwebsite:gridwikiindex}
412
413
414
415 \subsubsection{Plug-ins}
416 \label{lcmaps_plugins_section}
417 Site admins can configure plug-ins to enforce possible mappings to execution environments that a user can receive.
418 The plug-ins that LCMAPS executes must all exit successfully before authorization can continue. \cite{nikhefwebsite:gridwikiindex}
419 Here are the plug-ins \cite{lcmaps_apidoc} available at the time of writing.
420
421 \begin{description}
422 %\item[Gridlist]{A plug-in that maps users to pool accounts using the gridmapfile \cite{gridmapfile}}
423 \item[Local account]{Maps the supplied user credentials (i.e. a Subject DN or VOMS-signed FQANs) to a local user account on a target system.}
424 \item[Pool account]{Maps the supplied user credentials (i.e. a Subject DN or VOMS-signed FQANs) to a pool account on a target system.}
425 \item[POSIX enforcement]{A plug-in that applies acquired credential information to procure a Unix user account on a target system and verifies that the account was successfully attained.}
426 \item[LDAP enforcement]{A plug-in that applies acquired credential information in a target LDAP database.}
427 \item[Verify proxy]{This plug-in can verify the validity and authenticity of the incoming Grid credentials (a proxy certificate), and enforce life time constraints on the proxy.}
428 \item[SCAS client]{This plug-in delegates the mapping functionality to the \textit{Site Central Authorization Service} (SCAS).
429 It interacts with the SCAS or other any interoperable service using the SAML2XACML2 \cite{authzinterop} profile for Authorization Interoperability.}
430 \end{description}
431
432 \subsection{SAML2XACML2}
433 The \textit{SAML2XACML2 profile for Authorization Interoperability in Grids} \cite{authzinterop} is an XML-based protocol that has been agreed upon by various Grid middleware vendors \cite{authzinterop}.
434 SAML2XACML2 defines a protocol to communicate the delegation of authorization enforcement securely.
435 It is based on the SAML \cite{saml} profile for XACML v2.0 \cite{xacml}.
436
437 The conditions that should be enforced by a Grid middleware service like LCMAPS are expressed as XACML Obligations.
438 An Obligation that gLExec might fulfil would be a Unix \textit{uid} and/or \textit{gid}s.
439
440 Obligations are name-spaced identifiers that can contain attributes.
441 Returned XACML obligations are non-repudiable (undeniable) and must be handled by the client who receives them.
442 The XACML convention is to abort the authorization (and mapping) process if the client cannot meet the obligations set by the service.
443
444 \subsection{SCAS}
445 The \textit{Site Central Authorization Service} makes authorization and mapping decisions centrally.
446 %It uses HTTPS authentication to authenticate a client, based on the credentials in their Grid certificate. %(as regular user or pilot job user) and present user credentials.
447 %The service is a front-end to the LCAS and LCMAPS frameworks and uses HTTPS with mutual authentication to setup a session in which a SAML2-XACML2 \cite{authzinterop} request is sent.
448 It allows site administrators to centrally manage LCAS and LCMAPS configurations for multiple clusters.
449
450 Other services can interact with the SCAS by sending SAML2-XACML2 requests through an HTTPS connection with mutual authentication to receive authorization and mapping decisions.
451 It uses LCAS and LCMAPS as a back-end to actually enforce this, so as to be as transparent as possible to deploy.
452
453 The SCAS is specifically tailored to solve the use case involving pilot job frameworks. (Please see appendix \ref{use_case_pilot_job}.)
454
455 The SCAS will authorize the pilot job framework production manager and it will authorize the payload user using the LCAS framework.
456 Upon successful authorization the user credentials of the payload will be mapped to site-local credentials by LCMAPS and returned in a SAML2-XACML2 \cite{authzinterop} response.
457
458 \glossary{name={SCAS}, description={Site Central Authorization Service}}
459
460
461 \begin{figure}[hp]
462 \centering
463 \includegraphics[width=\textwidth]{scas}
464 \caption[SCAS diagram]%
465 {A diagram showing the architecture of a SCAS-based authenticating \& authorization installation}
466 \label{fig:scas}
467 \end{figure}
468
469
470
471 \subsection{Limitations of existing frameworks}
472 The frameworks lack the (native) support to process and pass through anything other than X.509 related information, VOMS credentials and Unix \textit{uid}s/\textit{gid}s.
473 New use cases demand the possibility of passing other credentials and arbitrary information to operate.
474 \begin{description}
475 % Behalve de unix credentials zoals we die nu hebben doorgeven, we ook use-cases om dynamisch priority queues en priority scheduling te kunnen doen in verschillende typen batch systems met verschillende batch system scheduler.
476 %\item Software design overly complex, difficult to maintain.
477 % Alleen evaluation manager
478 %\item Strongly oriented towards existing use cases.
479 %\item Unable to handle new use cases.
480 \item[Strong binding to X.509 certificates, VOMS credentials, and Unix \textit{uid}s/\textit{gid}s.]{
481 This limits the types of systems and services the middleware frameworks can natively interact with.
482 For example mapping of user credentials to Virtual Machine images is something that can't be supported natively.
483 }
484 %\item[No facility to interact with scheduling services]
485 \item[Does not facilitate direct low-level interaction with batch systems and schedulers]{
486 A desired functionality is the on-demand creation of priority queues.
487 It should also be possible to manipulate existing scheduling configurations.
488 }
489 \item[No facility to interact with virtualization frameworks]{
490 %kijk naar sander's e-mail van vanochtend (15 oct. 11:11) onder taken.
491 %describe interaction
492 To enable the scheduling of Virtual Machine execution, a connection to existing virtualization frameworks must be facilitated.
493 The \textit{Open Cloud Computing Interface} (OCCI) API \cite{occi} or OpenNebula toolkit \cite{opennebula} could be incorporated to enable scheduling of virtual machine execution.
494 % plug-in voor het batch systeem
495 }
496
497 \item[No facility to interact with batch-systems in an arbitrary way]{
498 % Op ieder cluster systeem heb je allerlei trucjes om je systeem in leven te houden, dit maakt een hook voor je.
499 %Het idee is dat je met perl/python scripts systeembeheerders mogelijkheden geven om systeem-specifieke handelingen uit te kunenn voeren. bijv. interacties met lokale accounting systemen
500 Because every cluster configuration is different it would be very beneficial to let system administrators hook their management scripts into the framework.
501 Adding support for high-level scripting languages like Perl or Python and providing them access to the internal plug-in API should be an effective way to allow this.
502 }
503 % We hebben een datastore. Datastore is toegespitst op X509,VOMS, en Unix credentials
504 %\item Inability to facilitate a shared data store for plug-ins executed in the framework.
505 % LCAS/LCMAPS hebbben wel een data store, om gegevens te delen
506 % Maar dat ze te specifiek zijn voor bepaalde toepassing
507 % Toegespitst op bepaalde use cases.
508 % Het moet generiek worden.
509
510
511
512 % Uitwijden over wat we van plan zijn
513 % Alles is georienteerd op x509 plus voms naar unix credentials.
514 % MEER ARGUMENTATIE
515
516 %\item Opaque and non-intuitive due to the above.
517 \end{description}
518
519 %\chapter{The new authorization framework}
520 %\chapter{The EES Execution Framework}
521 \pagebreak
522 \section{Argus: the new authorization framework}
523
524 Argus is the new gLite authorization framework and aims to improve interoperability between Grid services.
525 The Argus framework separates the roles and tasks as performed by the SCAS system into more granular and abstract services.
526 It is designed to be more modular than SCAS, and should be able to handle new use cases.
527 %, like what, why and how?
528 % Abstracter, meerdere componenten. duidelijke rolverdeling
529 % Waarom waarom waarom???
530 %
531
532 \subsection{Components of the Argus framework}
533 %\section{Architecture of the Argus Authorization Services}
534
535 \subsubsection{Policy Enforcement Point (PEP)}
536 The \textit{Policy Enforcement Point} is the client to the authorization service.
537 It generates an authorization request and forwards it to the PDP for evaluation.
538 The PDP responds with a decision, and a set of obligations the PEP must fulfil.
539 %krijgt een beslissing terug, met obligations die 'ie moet verwerken
540
541 \subsubsection{Policy Decision Point (PDP)}
542 The \textit{Policy Decision Point} is a policy evaluation engine.
543 The PDP receives authorization requests from Policy Enforcement Points and evaluates these requests against authorization policies retrieved from the PAP.
544 It returns its response to the PEP, and interacts with an EES to procure (specific) execution environments.
545
546 %antwoord wordt teruggegeven aan een PEP
547
548 \subsubsection{Policy Administration Point (PAP)}
549 The \textit{Policy Administration Point} provides tools to author, store and manage authorization policies.
550 This service can interact with other PAPs, and can combine external policies with local ones.
551 Interaction with other PAPs can be useful to coordinate policies in dealing with security issues.
552 It provides managed policies to other authorization service components, such as the PDP.
553
554 % interact met externe (andere PAP's). (Bijv OSCT)
555 % Externe policies kan 'ie combineren met de lokale policies
556
557 \subsubsection{Execution Environment Service (EES)}
558 %The \textit{Execution Environment Service}.
559 The role of the EES is to ensure that an appropriate site-specific execution environment is procured based on the site-agnostic obligations and attributes it receives as input in the form of SAML2-XACML2 requests.
560 It responds to requests from the PDP, but can also act as a standalone service.
561 It should be able to interact with many kinds of services and systems, for instance:
562 \begin{itemize}
563 \item Mapping users to pool accounts on Unix systems
564 %\item Interacting with the Maui scheduler to reconfigure a queue (e.g. changing scheduling configuration, creating a queue with certain requirements and moving a queue)
565 \item Add or change batch system queues
566 \item Procuring a VM environment through a virtualization framework
567 \item Executing arbitrary scripts local to the site for management purposes, as an addition to site-specific tooling or to be able to support specific use cases for which native support is not available
568 \end{itemize}
569
570 \begin{figure}[hp]
571 \centering
572 \includegraphics[width=\textwidth]{argus}
573 \caption[Argus diagram]
574 {A diagram showing the architecture of Argus authorization framework. As you can see, the SCAS client has been replaced by a PEP client, which provides access to the rest of the middleware framework}
575 \label{fig:argus}
576 \end{figure}
577
578 % interacties met andere dingen
579 % Pool account mapping
580 % Maui queue
581 % VM procurement
582 % OpenNebula
583 % arbitrary script execution
584
585 %\subsection{Policy Information Point (PIP)}
586 %The \textit{Policy Information Point} ...
587
588 \glossary{name={EES}, description={Execution Environment Service}}
589 \nomenclature{EES}{Execution Environment Service}
590
591 \glossary{name={PDP}, description={Policy Decision Point}}
592 \nomenclature{PDP}{Policy Decision Point}
593
594 \glossary{name={PAP}, description={Policy Administration Point}}
595 \nomenclature{PAP}{Policy Administration Point}
596
597 \glossary{name={PIP}, description={Policy Information Point}}
598 \nomenclature[]{PIP}{Policy Information Point}
599

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