XRI Resolution 2.0

This document defines a simple generic format for resource description (XRDS documents), a protocol for obtaining XRDS documents from HTTP(S) URIs, and generic and trusted protocols for resolving Extensible Resource Identifiers (XRIs) using XRDS documents and HTTP(S) URIs. These protocols are intended for use with both HTTP(S) URIs as defined in [RFC2616] and with XRIs as defined by Extensible Resource Identifier (XRI) Syntax Version 2.0 [XRISyntax] or higher. For a dictionary of XRIs defined to provide standardized identifier metadata, see Extensible Resource Identifier (XRI) Metadata Version 2.0 [XRIMetadata]. For a basic introduction to XRIs, see the XRI 2.0 FAQ [XRIFAQ].

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Table of Contents

1 Introduction.............................................................................................................................. 11

1.1 Overview of XRI Resolution Architecture................................................................................... 11

1.2 Structure of this Specification.................................................................................................. 14

1.3 Terminology and Notation........................................................................................................ 15

1.4 Examples............................................................................................................................... 15

1.5 Normative References............................................................................................................. 15

1.6 Non-Normative References...................................................................................................... 16

2 Conformance........................................................................................................................... 17

2.1 Conformance Targets.............................................................................................................. 17

2.2 Conformance Claims............................................................................................................... 17

2.3 XRDS Clients.......................................................................................................................... 17

2.4 XRDS Servers........................................................................................................................ 17

2.5 XRI Local Resolvers................................................................................................................ 18

2.5.1 Generic............................................................................................................................ 18

2.5.2 HTTPS............................................................................................................................. 18

2.5.3 SAML.............................................................................................................................. 18

2.6 XRI Proxy Resolvers............................................................................................................... 18

2.6.1 Generic............................................................................................................................ 18

2.6.2 HTTPS............................................................................................................................. 18

2.6.3 SAML.............................................................................................................................. 18

2.7 XRI Authority Servers.............................................................................................................. 19

2.7.1 Generic............................................................................................................................ 19

2.7.2 HTTPS............................................................................................................................. 19

2.7.3 SAML.............................................................................................................................. 19

2.8 Extensions............................................................................................................................. 19

2.9 Language............................................................................................................................... 19

3 Namespaces............................................................................................................................ 20

3.1 XRI Namespaces for XRI Resolution........................................................................................ 20

3.1.1 XRIs Reserved for XRI Resolution..................................................................................... 20

3.1.2 XRIs Assigned to XRI Resolution Service Types................................................................ 20

3.2 XML Namespaces for XRI Resolution....................................................................................... 21

3.3 Media Types for XRI Resolution............................................................................................... 21

4 XRDS Documents.................................................................................................................... 23

4.1 XRDS and XRD Namespaces and Schema Locations............................................................... 23

4.2 XRD Elements and Attributes.................................................................................................. 23

4.2.1 Management Elements..................................................................................................... 25

4.2.2 Trust Elements................................................................................................................. 26

4.2.3 Synonym Elements.......................................................................................................... 27

4.2.4 Service Endpoint Descriptor Elements.............................................................................. 27

4.2.5 Service Endpoint Trust Elements....................................................................................... 29

4.2.6 Service Endpoint Selection Elements................................................................................ 29

4.3 XRD Attribute Processing Rules.............................................................................................. 30

4.3.1 ID Attribute...................................................................................................................... 30

4.3.2 Version Attribute.............................................................................................................. 30

4.3.3 Priority Attribute............................................................................................................... 30

4.4 XRI and IRI Encoding Requirements......................................................................................... 31

5 XRD Synonym Elements........................................................................................................... 32

5.1 Query Identifiers...................................................................................................................... 32

5.1.1 HTTP(S) URI Query Identifiers........................................................................................... 32

5.1.2 XRI Query Identifiers......................................................................................................... 32

5.2 Synonym Elements................................................................................................................. 33

5.2.1 LocalID............................................................................................................................ 33

5.2.2 EquivID........................................................................................................................... 33

5.2.3 CanonicalID..................................................................................................................... 34

5.2.4 CanonicalEquivID............................................................................................................. 34

5.3 Redirect and Ref Elements...................................................................................................... 35

5.4 XRD Equivalence.................................................................................................................... 35

5.5 Synonym Verification.............................................................................................................. 36

5.6 Synonym Selection................................................................................................................. 36

6 Discovering an XRDS Document from an HTTP(S) URI............................................................... 37

6.1 Overview................................................................................................................................ 37

6.2 HEAD Protocol....................................................................................................................... 37

6.3 GET Protocol.......................................................................................................................... 37

7 XRI Resolution Flow................................................................................................................. 39

8 Inputs and Outputs................................................................................................................... 41

8.1 Inputs..................................................................................................................................... 41

8.1.1 QXRI (Authority String, Path String, and Query String)........................................................ 43

8.1.2 Resolution Output Format................................................................................................. 43

8.1.3 Service Type.................................................................................................................... 44

8.1.4 Service Media Type.......................................................................................................... 45

8.2 Outputs.................................................................................................................................. 45

8.2.1 XRDS Document.............................................................................................................. 47

8.2.2 XRD Element................................................................................................................... 47

8.2.3 URI List............................................................................................................................ 48

8.2.4 HTTP(S) Redirect.............................................................................................................. 48

9 Generic Authority Resolution Service......................................................................................... 49

9.1 XRI Authority Resolution.......................................................................................................... 49

9.1.1 Service Type and Service Media Type............................................................................... 49

9.1.2 Protocol.......................................................................................................................... 50

9.1.3 Requesting an XRDS Document using HTTP(S)................................................................. 52

9.1.4 Failover Handling............................................................................................................. 53

9.1.5 Community Root Authorities............................................................................................. 54

9.1.6 Self-Describing XRDS Documents.................................................................................... 55

9.1.7 Qualified Subsegments.................................................................................................... 55

9.1.8 Cross-References............................................................................................................. 56

9.1.9 Selection of the Next Authority Resolution Service Endpoint.............................................. 56

9.1.10 Construction of the Next Authority URI............................................................................. 57

9.1.11 Recursing Authority Resolution........................................................................................ 57

9.2 IRI Authority Resolution........................................................................................................... 58

9.2.1 Service Type and Media Type........................................................................................... 58

9.2.2 Protocol.......................................................................................................................... 58

9.2.3 Optional Use of HTTPS.................................................................................................... 58

10 Trusted Authority Resolution Service......................................................................................... 60

10.1 HTTPS.................................................................................................................................. 60

10.1.1 Service Type and Service Media Type............................................................................. 60

10.1.2 Protocol......................................................................................................................... 60

10.2 SAML................................................................................................................................... 60

10.2.1 Service Type and Service Media Type............................................................................. 61

10.2.2 Protocol......................................................................................................................... 61

10.2.3 Recursing Authority Resolution........................................................................................ 62

10.2.4 Client Validation of XRDs............................................................................................... 63

10.2.5 Correlation of ProviderID and KeyInfo Elements............................................................... 64

10.3 HTTPS+SAML....................................................................................................................... 64

10.3.1 Service Type and Service Media Type............................................................................. 64

10.3.2 Protocol......................................................................................................................... 65

11 Proxy Resolution Service.......................................................................................................... 66

11.1 Service Type and Media Types.............................................................................................. 66

11.2 HXRIs................................................................................................................................... 66

11.3 HXRI Query Parameters......................................................................................................... 67

11.4 HXRI Encoding/Decoding Rules............................................................................................. 68

11.5 HTTP(S) Accept Headers....................................................................................................... 70

11.6 Null Resolution Output Format............................................................................................... 70

11.7 Outputs and HTTP(S) Redirects.............................................................................................. 70

11.8 Differences Between Proxy Resolution Servers....................................................................... 71

11.9 Combining Authority and Proxy Resolution Servers................................................................. 71

12 Redirect and Ref Processing..................................................................................................... 72

12.1 Cardinality............................................................................................................................. 74

12.2 Precedence........................................................................................................................... 74

12.3 Redirect Processing.............................................................................................................. 75

12.4 Ref Processing..................................................................................................................... 76

12.5 Nested XRDS Documents..................................................................................................... 77

12.5.1 Redirect Examples......................................................................................................... 77

12.5.2 Ref Examples................................................................................................................ 81

12.6 Recursion and Backtracking................................................................................................... 84

13 Service Endpoint Selection....................................................................................................... 85

13.1 Processing Rules.................................................................................................................. 85

13.2 Service Endpoint Selection Logic........................................................................................... 87

13.3 Selection Element Matching Rules.......................................................................................... 88

13.3.1 Selection Element Match Options.................................................................................... 88

13.3.2 The Match Attribute......................................................................................................... 88

13.3.3 Absent Selection Element Matching Rule......................................................................... 89

13.3.4 Empty Selection Element Matching Rule.......................................................................... 89

13.3.5 Multiple Selection Element Matching Rule........................................................................ 89

13.3.6 Type Element Matching Rules......................................................................................... 89

13.3.7 Path Element Matching Rules.......................................................................................... 90

13.3.8 MediaType Element Matching Rules................................................................................ 92

13.4 Service Endpoint Matching Rules........................................................................................... 92

13.4.1 Service Endpoint Match Options..................................................................................... 92

13.4.2 Select Attribute Match Rule............................................................................................. 92

13.4.3 All Positive Match Rule................................................................................................... 92

13.4.4 Default Match Rule......................................................................................................... 92

13.5 Service Endpoint Selection Rules........................................................................................... 93

13.5.1 Positive Match Rule........................................................................................................ 93

13.5.2 Default Match Rule......................................................................................................... 93

13.6 Pseudocode......................................................................................................................... 93

13.7 Construction of Service Endpoint URIs................................................................................... 95

13.7.1 The append Attribute...................................................................................................... 95

13.7.2 The uric Parameter.......................................................................................................... 96

14 Synonym Verification................................................................................................................ 97

14.1 Redirect Verification.............................................................................................................. 97

14.2 EquivID Verification............................................................................................................... 97

14.3 CanonicalID Verification......................................................................................................... 98

14.3.1 HTTP(S) URI Verification Rules........................................................................................ 99

14.3.2 XRI Verification Rules..................................................................................................... 99

14.3.3 CanonicalEquivID Verification......................................................................................... 99

14.3.4 Verification Status Attributes......................................................................................... 100

14.3.5 Examples..................................................................................................................... 101

15 Status Codes and Error Processing......................................................................................... 106

15.1 Status Elements.................................................................................................................. 106

15.2 Status Codes...................................................................................................................... 106

15.3 Status Context Strings......................................................................................................... 109

15.4 Returning Errors in Plain Text or HTML.................................................................................. 109

15.5 Error Handling in Recursing and Proxy Resolution................................................................. 109

16 Use of HTTP(S)...................................................................................................................... 110

16.1 HTTP Errors........................................................................................................................ 110

16.2 HTTP Headers..................................................................................................................... 110

16.2.1 Caching........................................................................................................................ 110

16.2.2 Location....................................................................................................................... 110

16.2.3 Content-Type................................................................................................................ 110

16.3 Other HTTP Features............................................................................................................ 110

16.4 Caching and Efficiency........................................................................................................ 111

16.4.1 Resolver Caching.......................................................................................................... 111

16.4.2 Synonyms.................................................................................................................... 111

17 Extensibility and Versioning.................................................................................................... 112

17.1 Extensibility........................................................................................................................ 112

17.1.1 Extensibility of XRDs.................................................................................................... 112

17.1.2 Other Points of Extensibility.......................................................................................... 113

17.2 Versioning........................................................................................................................... 113

17.2.1 Version Numbering....................................................................................................... 113

17.2.2 Versioning of the XRI Resolution Specification...........................................