Cursor-based Pagination of SCIM Resources
draft-peterson-scim-cursor-pagination-00

Abstract

The System for Cross-domain Identity Management (SCIM) protocol supports the retrieval of core identity resources such as users and groups. In order to avoid overwhelming the SCIM client or service provider, SCIM defines index and count pagination query parameters that can be used "page through" large numbers of resources. For some SCIM service providers there are advantages in implementing cursor-based pagination as an alternative to index-based pagination. This document defines a simple extension to the SCIM protocol and core schema to assure interoperability of SCIM implementations that need to realize the advantages cursor-based pagination.

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1. Introduction

System for Cross-domain Identity Management (SCIM) protocol [RFC7644] supports the retrieval of core identity resources such as users and groups. When many resources exist, two strategies may be employed to help to avoid overwhelming the SCIM client and service provider. First, SCIM supports the use of query filters. A query filter allows the SCIM client to constrain the results returned to just the subset of resources that are needed by the client. Second, SCIM supports the ability to "page through" large result sets using index/count pagination parameters.

Not only is filtering an OPTIONAL capability,for service providers, it is also a very common for SCIM clients to not to use a query filter in order to intentionally to retrieve all resources. Therefore, pagination of results (more so than filtering) is a primary scalability mechanism for SCIM service providers.

The two most common patterns for result pagination in HTTP-based protocols are: index-based pagination, and cursor-based pagination. Both approaches have advantages and disadvantages. For web applications that also provide a application-specific Web API, the decision for which result pagination approach to use in the Web API is often dictated by the capabilities and optimizations of the underlying application database technology, or by strongly held preference of software developers.

Implementation of a SCIM service provider is often made as a companion service along side an already existing application-specific Web API. If cusor-based pagination is already used in an existing application, it can be difficult to create a companion SCIM implementation that uses existing application code paths. For these applications, the mismatch in pagination approaches (index-based vs. cursor-based) is an impediment to SCIM implementation.

This document defines a simple extension to the SCIM protocol and core schema that adds support for cursor-based pagination. Support for cursor-based pagination in SCIM encourages broader cross-application identity management interoperiablity by encouraging SCIM implementations for applications where cursor-based pagination is preferred.

1.1. Notational 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 RFC 2119 [RFC2119].

2. Query Parameters and Response Attributes

The following table describes the URL pagination parameters for cursor-based pagination:

          
   GET /Users?count=10
   Host: example.com
   Accept: application/scim+json
   Authorization: Bearer U8YJcYYRMjbGeepD

        

          
   {
       "totalResults":100,
       "nextCursor":"VZUTiyhEQJ94IR",
       "schemas":["urn:ietf:params:scim:api:messages:2.0:ListResponse"],
       "Resources":[{
        ...
       }]
   }

        

          
   GET /Users?cursor=VZUTiyhEQJ94I&count=10
   Host: example.com
   Accept: application/scim+json
   Authorization: Bearer U8YJcYYRMjbGeepD

        

          
   GET /ServiceProviderConfig
   Host: example.com
   Accept: application/scim+json

        

          
   {
      "schemas": [
         "urn:ietf:params:scim:schemas:core:2.0:ServiceProviderConfig"],

      ...

      "pagination": {
         "cursor":true
      },

      ...
   }