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Merge pull request #941 from matyasselmeci/pr/SOFTWARE-5077.moartokens
Token overview (SOFTWARE-5077)
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‎docs/security/tokens/overview.md

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DateReviewed: 2022-03-10
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Bearer Token Overview
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=====================
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Token-based Authentication and Authorization Infrastructure (AAI) is a security method
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that is intended as the replacement for X.509 for accessing compute and storage resources.
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This document will describe "bearer tokens," which are one of the components of Token AAI;
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bearer tokens are the type of token that server software such as HTCondor and XRootD will primarily interact with.
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A bearer token (sometimes called an "access token") is a short-lived credential,
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performing a similar role as a grid proxy did in X.509.
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X.509 proxies established identity (the DN in your subject) and group membership (VOMS FQANs).
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Servers made decisions about access based on those properties.
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Tokens also have 'scope' which can restrict the actions that can be done with the token.
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For example, a token used for storage access can restrict the files that can be read to a particular directory tree.
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Instead of using a single proxy, a job may have multiple tokens.
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For example the job could have one token granting it the ability to be run;
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it could have a token for read access to an input dataset, and a token for write access to a results directory.
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Token Components
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----------------
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Bearer tokens are credential strings in the [JSON Web Token (JWT)](https://jwt.io) format.
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A JWT consists of a JSON header, a JSON payload, and a signature that can be verified.
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The payload contains a number of fields, called "claims", that describe the token and what it can access.
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There are two JWT-based token standards that can be used with OSG software: [SciTokens](https://scitokens.org)
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and [WLCG Tokens](https://github.com/WLCG-AuthZ-WG/common-jwt-profile/blob/master/profile.md).
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These standards describe the claims that are used in the payload of the JWT.
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SciTokens and WLCG Tokens are similar standards and have some common claims:
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**Issuer ("iss")**
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The issuer identifies the organization that issued the token.
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An issuer looks like an HTTPS URL;
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this URL must be valid and publicly accessible as they are used by site services to validate the token.
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Token issuers will be [described below](#issuer).
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**Subject ("sub")**
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The subject identifies an entity (which could be a human or a robot) that owns the token.
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Unlike the subject of an X.509 certificate, a token subject does not need to be globally unique,
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only unique to the issuer.
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Subjects will be [elaborated on below](#subject).
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**Issued-at ("iat"), not-before ("nbf"), expiration ("exp")**
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These claims are Unix timestamps that specify when the token was issued, and its lifespan.
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**Audience ("aud")**
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The audience is a server (or a JSON list of servers) that the token may be used on;
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it is typically a hostname, host:port, or URI.
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For example a token used for submitting a job to a CE would have
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`<CE FQDN>:<CE PORT>` in the `aud` claim.
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The special values `ANY` (SciTokens) or `https://wlcg.cern.ch/jwt/v1/any` (WLCG Tokens) allow the token to be
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used on any server.
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**Scope ("scope")**
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The scope limits the actions that can be made using the token.
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The format of the scope claim differs between SciTokens and WLCG Tokens;
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scopes in use by OSG services will be [listed below](#scopes).
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WLCG Tokens may have a `wlcg.group` instead of a scope, [as described below](#wlcg-groups).
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### Issuer ###
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To generate bearer tokens, a collaboration must adminster at least one "token issuer" to issue tokens to their users.
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In addition to generating and signing tokens, token issuers provide a public endpoint that can be used to validate an
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issued token,
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e.g. an OSG Compute Entrypoint (CE) will contact the token issuer to authorize a bearer token used for pilot job
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submission.
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The issuer is listed in the `iss` claim; this should be an HTTPS URL of a web server.
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This server must have the public key that can be used to validate the token in a well-known location,
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as described by the [OpenID Connect Discovery standard](https://openid.net/specs/openid-connect-discovery-1_0.html).
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If the issuer is down, or the the public key cannot be downloaded, the token cannot be verified
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and will be rejected.
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Note that most clients will cache the public key.
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In order to ease the token transition, the current cache lifetime is 4 days,
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but at some point this will be lowered to a few hours.
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A collaboration may have more than one token issuer,
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but a single token issuer should never serve more than one collaboration.
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The issuer claim should be able to uniquely identify the collaboration that identifies the token.
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### Subject ###
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The subject is listed in the `sub` claim and should be unique, stable identifier that corresponds to a user (human)
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or a service (robot or pilot job submission).
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A subject does not need to be globally unique but it must be unique to the issuer.
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The subject, when combined with the issuer, will give a globally unique identity
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that can be used for mapping, banning, accounting, monitoring, auditing, or tracing.
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!!! note
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Due to privacy concerns, the subject may be a randomly generated string, hash, UUID, etc.,
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that does not contain any personally identifying information.
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Tracing a token to a user or service may require contacting the issuer.
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### Scopes ###
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The `scope` claim is a space-separated list of authorizations that should be granted to the bearer.
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Scopes utilized by OSG services include the following:
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| **Capability** | **SciTokens scope** | **WLCG scope** |
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|------------------|---------------------|------------------------------------------------|
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| HTCondor `READ` | `condor:/READ` | `compute.read` |
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| HTCondor `WRITE` | `condor:/WRITE` | `compute.modify compute.cancel compute.create` |
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| XRootD read | `read:<PATH>` | `storage.read:<PATH>` |
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| XRootD write | `write:<PATH>` | `storage.modify:<PATH>` |
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Replacing `<PATH>` with a path to the storage location that the bearer should be authorized to access.
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A SciToken must have a non-empty scope, or it cannot be used to do anything.
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### WLCG Groups ###
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A WLCG Token may have a `wlcg.groups` claim instead of a scope.
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The `wlcg.groups` claim is a comma and space separated list of collaboration groups.
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The format of these groups are similar to VOMS FQANs: `/<collaboration>[/<group>][/Role=<role>]`,
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replacing `<collaboration>`, `<group>`, and `<role>` with the collaboration, group, and role, respectively, where the
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group and role are optional.
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For example, the following groups and roles have been used by the ATLAS and CMS collaborations:
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```
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/atlas/
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/atlas/usatlas
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/cms/Role=pilot
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/cms/local/Role=pilot
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```
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If an incoming (pre-routed) pilot on a CE has a token, it will have the following classad attributes:
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| Attribute | Meaning |
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|------------------|-------------------------------------|
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| AuthTokenId | A UUID of the token |
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| AuthTokenIssuer | The URL of the issuer of the token |
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| AuthTokenScopes | Any scope restrictions on the token |
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| AuthTokenSubject | The 'sub' field of the token |
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| Attribute | Meaning |
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|------------------|--------------------------------------|
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| AuthTokenId | A UUID of the token |
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| AuthTokenIssuer | The URL of the issuer of the token |
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| AuthTokenScopes | Any scope restrictions on the token |
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| AuthTokenSubject | The `sub` claim of the token |
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| AuthTokenGroups | The `wlcg.groups`, if any, claim of the token |
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(A pre-routed job is a job without `RoutedJob=True` in its classad.)
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| IceCube | Undergoing testing |
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| LIGO | Undergoing testing |
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| OSG | N/A |
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Help
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----
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To get assistance, please use the [this page](https://opensciencegrid.org/docs/common/help/).
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References and Links
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--------------------
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- [Troubleshooting Tokens](using-tokens.md#troubleshooting-tokens)
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- [OSG Technology - Collaborations and Bearer Tokens](https://opensciencegrid.org/technology/policy/collab-bearer-tokens/)
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- [JSON Web Tokens](https://jwt.io) - includes token decoder
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- [SciTokens](https://scitokens.org)
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- [SciToken Claims and Scopes Language](https://scitokens.org/technical_docs/Claims)
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- [SciTokens Demo](https://demo.scitokens.org/) - includes token generator, verifier, and links to libraries
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- [WLCG Common JWT Profiles](https://github.com/WLCG-AuthZ-WG/common-jwt-profile/blob/master/profile.md)

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