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Network Working Group                                        N. WilliamsRequest for Comments: 5588                                           SunCategory: Standards Track                                      July 2009Generic Security Service Application Program Interface (GSS-API)Extension for Storing Delegated CredentialsAbstract   This document defines a new function for the Generic Security Service   Application Program Interface (GSS-API), which allows applications to   store delegated (and other) credentials in the implicit GSS-API   credential store.  This is needed for GSS-API applications to use   delegated credentials as they would use other credentials.Status of This Memo   This document specifies an Internet standards track protocol for the   Internet community, and requests discussion and suggestions for   improvements.  Please refer to the current edition of the "Internet   Official Protocol Standards" (STD 1) for the standardization state   and status of this protocol.  Distribution of this memo is unlimited.Copyright Notice   Copyright (c) 2009 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 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.Table of Contents1. Introduction ....................................................22. Conventions Used in This Document ...............................33. GSS_Store_cred() ................................................34. C-Bindings ......................................................55. Examples ........................................................66. Security Considerations .........................................67. Normative References ............................................7Williams                    Standards Track                     [Page 1]

RFC 5588                    GSS_Store_cred()                   July 20091.  Introduction   The GSS-API [RFC2743] clearly assumes that credentials exist in an   implicit store whence they can be acquired using GSS_Acquire_cred()   and GSS_Add_cred() or through use of the default credential.   Multiple credential stores may exist on a given host, but only one   store may be accessed by GSS_Acquire_cred() and GSS_Add_cred() at any   given time.   This assumption can be seen in Sections1.1.1.2 and1.1.1.3 of   [RFC2743] as well as inSection 3.5 of [RFC2744].   Applications may be able to change the credential store from which   credentials can be acquired, either by changing user contexts (where   the applications have the privilege to do so) or by other means   (where a user may have multiple credential stores).   Some GSS-API acceptor applications always change user contexts, after   accepting a GSS-API security context and making appropriate   authorization checks, to the user context corresponding to the   initiator principal name or to a context requested by the initiator.   The means by which credential stores are managed are generally beyond   the scope of the GSS-API.   In the case of delegated credential handles however, such credentials   do not exist in the acceptor's credential store or in the credential   stores of the user contexts to which the acceptor application might   change.  The GSS-API provides no mechanism by which delegated   credential handles can be made available for acquisition through   GSS_Acquire_cred()/GSS_Add_cred().  The GSS-API also does not provide   any credential import/export interfaces like the GSS-API context   import/export interfaces.   Thus, acceptors are limited to making only direct use of delegated   credential handles and only with GSS_Init_sec_context(),   GSS_Inquire_cred*(), and GSS_Release_cred().  This limitation is   particularly onerous on Unix systems where a call to exec() to   replace the process image obliterates any delegated credentials   handle that may exist in that process.   In order to make delegated credentials generally as useful as   credentials that can be acquired with GSS_Acquire_cred() and   GSS_Add_cred(), a primitive is needed that allows storing of   credentials in the implicit credential store.  We call this primitive   "GSS_Store_cred()".Williams                    Standards Track                     [Page 2]

RFC 5588                    GSS_Store_cred()                   July 20092.  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.  GSS_Store_cred()   Inputs:   o  input_cred_handle CREDENTIAL HANDLE, -- credential to store; MUST      NOT be GSS_C_NO_CREDENTIAL.   o  cred_usage INTEGER -- 0=INITIATE-AND-ACCEPT, 1=INITIATE-ONLY,      2=ACCEPT-ONLY.   o  desired_mech_element OBJECT IDENTIFIER, -- if GSS_C_NULL_OID, then      store all the elements of the input_cred_handle, otherwise, store      only the element of the corresponding mechanism.   o  overwrite_cred BOOLEAN, -- if TRUE, replace any credential for the      same principal in the credential store.   o  default_cred BOOLEAN -- advisory input; if TRUE, make the stored      credential available as the default credential (for acquisition      with GSS_C_NO_NAME as the desired name or for use as      GSS_C_NO_CREDENTIAL).   Outputs:   o  major_status INTEGER.   o  minor_status INTEGER.   o  mech_elements_stored SET OF OBJECT IDENTIFIER, -- the set of      mechanism OIDs for which credential elements were successfully      stored.   o  cred_usage_stored INTEGER -- like cred_usage, but indicates what      kind of credential was stored (useful when the cred_usage input      parameter is set to INITIATE-AND-ACCEPT).   Return major_status codes:   o  GSS_S_COMPLETE indicates that the credentials were successfully      stored.Williams                    Standards Track                     [Page 3]

RFC 5588                    GSS_Store_cred()                   July 2009   o  GSS_S_CREDENTIALS_EXPIRED indicates that the input credentials had      expired or expired before they could be stored.   o  GSS_S_NO_CRED indicates that no input credentials were given.   o  GSS_S_UNAVAILABLE indicates that the credential store is not      available.   o  GSS_S_DUPLICATE_ELEMENT indicates that an element of the input      credential could not be stored because a credential for the same      principal exists in the current credential store and the      overwrite_cred input argument was FALSE.   o  GSS_S_FAILURE indicates that the credential could not be stored      for some other reason.  The minor status code may provide more      information if a non-GSS_C_NULL_OID desired_mech_element was      given.   GSS_Store_cred() is used to store, in the current credential store, a   given credential that has either been acquired from a different   credential store or been accepted as a delegated credential.   Specific mechanism elements of a credential can be stored one at a   time by specifying a non-GSS_C_NULL_OID mechanism OID as the   desired_mech_element input argument; in which case, the minor status   output SHOULD have a mechanism-specific value when the major status   is not GSS_S_COMPLETE.   The initiator, acceptor, or both usages of the input credential may   be stored as per the cred_usage input argument.   The credential elements that were actually stored, when the major   status is GSS_S_COMPLETE, are indicated through the cred_usage_stored   and mech_elements_stored function outputs.   If credentials already exist in the current store for the principal   of the input_cred_handle, then those credentials are not replaced   with the input credentials unless the overwrite_cred input argument   is TRUE.   In the GSS-API, the default credential can be used by using   GSS_C_NO_CREDENTIAL or a CREDENTIAL handle acquired by calling   GSS_Acquire_cred() or GSS_Add_cred() with the desired_name input set   to GSS_C_NO_NAME.   If the default_cred input argument is TRUE, and the input credential   can be successfully stored, then the input credential SHOULD be   stored as the default credential (see above).Williams                    Standards Track                     [Page 4]

RFC 5588                    GSS_Store_cred()                   July 2009   If the current credential store has no default credential (see   above), then the implementation MAY make the stored credentials   available as the default credential regardless of the value of the   default_cred input argument.4.  C-Bindings   The C-Bindings for GSS_Store_cred() make use of types from and are   designed based on the style of the GSS-APIv2 C-Bindings [RFC2744].         OM_uint32 gss_store_cred(            OM_uint32         *minor_status,            gss_cred_id_t     input_cred_handle,            gss_cred_usage_t  cred_usage,            const gss_OID     desired_mech,            OM_uint32         overwrite_cred,            OM_uint32         default_cred,            gss_OID_set       *elements_stored,            gss_cred_usage_t  *cred_usage_stored)                        Figure 1   The two boolean arguments, 'overwrite_cred' and 'default_cred', are   typed as OM_uint32; 0 corresponds to FALSE, non-zero values   correspond to TRUE.Williams                    Standards Track                     [Page 5]

RFC 5588                    GSS_Store_cred()                   July 20095.  Examples   The intended usage of GSS_Store_cred() is to make delegated   credentials available to child processes of GSS-API acceptor   applications.  Example pseudo-code:      /*       * <GSS_Accept_sec_context() loop resulting in GSS_S_COMPLETE,       * an initiator name (hereafter, "src_name") and a delegated       * credential handle (hereafter "deleg_cred").>       *       * <"requested_username" is a username derived from the       * initiator name or explicitly requested by the initiator       * application.>       */      ...      if (authorize_gss_client(src_name, requested_username)) {         /*          * For Unix-type platforms this may mean calling setuid() and          * it may or may not also mean setting/unsetting such          * environment variables as KRB5CCNAME and what not -- all          * OS-specific details.          */         if (change_user_context(requested_username))            (void) gss_store_cred(&minor_status, deleg_cred,                                  GSS_C_INITIATE, actual_mech,                                  0, 1, NULL, NULL);         }         else ...      }      else ...6.  Security Considerations   Acceptor applications MUST only store delegated credentials into   appropriate credential stores and only after proper authorization of   the authenticated initiator principal to the requested service(s).   Acceptor applications that have no use for delegated credentials MUST   release them (such acceptor applications that use the GSS-API C-   Bindings may simply provide a NULL value for the   delegated_cred_handle argument to gss_accept_sec_context()).Williams                    Standards Track                     [Page 6]

RFC 5588                    GSS_Store_cred()                   July 20097.  Normative References   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate              Requirement Levels",BCP 14,RFC 2119, March 1997.   [RFC2743]  Linn, J., "Generic Security Service Application Program              Interface Version 2, Update 1",RFC 2743, January 2000.   [RFC2744]  Wray, J., "Generic Security Service API Version 2 :              C-bindings",RFC 2744, January 2000.Author's Address   Nicolas Williams   Sun Microsystems   5300 Riata Trace Ct   Austin, TX  78727   US   EMail: Nicolas.Williams@sun.comWilliams                    Standards Track                     [Page 7]