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Bearer Token Overview

Token-based Authentication and Authorization Infrastructure (AAI) is a security method that is intended as the replacement for X.509 for accessing compute and storage resources. This document will describe "bearer tokens," which are one of the components of Token AAI; bearer tokens are the type of token that server software such as HTCondor and XRootD will primarily interact with.

A bearer token (sometimes called an "access token") is a short-lived credential, performing a similar role as a grid proxy did in X.509. X.509 proxies established identity (the DN in your subject) and group membership (VOMS FQANs). Servers made decisions about access based on those properties. Tokens also have 'scope' which can restrict the actions that can be done with the token. For example, a token used for storage access can restrict the files that can be read to a particular directory tree. Instead of using a single proxy, a job may have multiple tokens. For example the job could have one token granting it the ability to be run; it could have a token for read access to an input dataset, and a token for write access to a results directory.

Token Components

Bearer tokens are credential strings in the JSON Web Token (JWT) format. A JWT consists of a JSON header, a JSON payload, and a signature that can be verified. The payload contains a number of fields, called "claims", that describe the token and what it can access.

There are two JWT-based token standards that can be used with OSG software: SciTokens and WLCG Tokens. These standards describe the claims that are used in the payload of the JWT.

SciTokens and WLCG Tokens are similar standards and have some common claims:

Issuer ("iss")

The issuer identifies the organization that issued the token. An issuer looks like an HTTPS URL; this URL must be valid and publicly accessible as they are used by site services to validate the token. Token issuers will be described below.

Subject ("sub")

The subject identifies an entity (which could be a human or a robot) that owns the token. Unlike the subject of an X.509 certificate, a token subject does not need to be globally unique, only unique to the issuer. Subjects will be elaborated on below.

Issued-at ("iat"), not-before ("nbf"), expiration ("exp")

These claims are Unix timestamps that specify when the token was issued, and its lifespan.

Audience ("aud")

The audience is a server (or a JSON list of servers) that the token may be used on; it is typically a hostname, host:port, or URI. For example a token used for submitting a job to a CE would have <CE FQDN>:<CE PORT> in the aud claim. The special values ANY (SciTokens) or https://wlcg.cern.ch/jwt/v1/any (WLCG Tokens) allow the token to be used on any server.

Scope ("scope")

The scope limits the actions that can be made using the token. The format of the scope claim differs between SciTokens and WLCG Tokens; scopes in use by OSG services will be listed below. WLCG Tokens may have a wlcg.group instead of a scope, as described below.

Issuer

To generate bearer tokens, a collaboration must adminster at least one "token issuer" to issue tokens to their users. In addition to generating and signing tokens, token issuers provide a public endpoint that can be used to validate an issued token, e.g. an OSG Compute Entrypoint (CE) will contact the token issuer to authorize a bearer token used for pilot job submission.

The issuer is listed in the iss claim; this should be an HTTPS URL of a web server. This server must have the public key that can be used to validate the token in a well-known location, as described by the OpenID Connect Discovery standard. If the issuer is down, or the the public key cannot be downloaded, the token cannot be verified and will be rejected. Note that most clients will cache the public key. In order to ease the token transition, the current cache lifetime is 4 days, but at some point this will be lowered to a few hours.

A collaboration may have more than one token issuer, but a single token issuer should never serve more than one collaboration. The issuer claim should be able to uniquely identify the collaboration that identifies the token.

Subject

The subject is listed in the sub claim and should be unique, stable identifier that corresponds to a user (human) or a service (robot or pilot job submission). A subject does not need to be globally unique but it must be unique to the issuer. The subject, when combined with the issuer, will give a globally unique identity that can be used for mapping, banning, accounting, monitoring, auditing, or tracing.

Note

Due to privacy concerns, the subject may be a randomly generated string, hash, UUID, etc., that does not contain any personally identifying information. Tracing a token to a user or service may require contacting the issuer.

Scopes

The scope claim is a space-separated list of authorizations that should be granted to the bearer. Scopes utilized by OSG services include the following:

Capability SciTokens scope WLCG scope
HTCondor READ condor:/READ compute.read
HTCondor WRITE condor:/WRITE compute.modify compute.cancel compute.create
XRootD read read:<PATH> storage.read:<PATH>
XRootD write write:<PATH> storage.modify:<PATH>

Replacing <PATH> with a path to the storage location that the bearer should be authorized to access.

A SciToken must have a non-empty scope, or it cannot be used to do anything.

WLCG Groups

A WLCG Token may have a wlcg.groups claim instead of a scope. The wlcg.groups claim is a comma and space separated list of collaboration groups. The format of these groups are similar to VOMS FQANs: /<collaboration>[/<group>][/Role=<role>], replacing <collaboration>, <group>, and <role> with the collaboration, group, and role, respectively, where the group and role are optional. For example, the following groups and roles have been used by the ATLAS and CMS collaborations:

/atlas/
/atlas/usatlas
/cms/Role=pilot
/cms/local/Role=pilot

Validating Tokens in Pilot Jobs

If an incoming (pre-routed) pilot on a CE has a token, it will have the following classad attributes:

Attribute Meaning
AuthTokenId A UUID of the token
AuthTokenIssuer The URL of the issuer of the token
AuthTokenScopes Any scope restrictions on the token
AuthTokenSubject The sub claim of the token
AuthTokenGroups The wlcg.groups, if any, claim of the token

(A pre-routed job is a job without RoutedJob=True in its classad.)

Note

A job may have both a token and an X.509 proxy. Presence of any x509* attributes does not indicate the absence of a token.

To see which authentication method was used for a job: - Examine the /var/log/condor-ce/AuditLog* files. - Find a line saying Submitting new job <JOBID> (where <JOBID> is a job ID like 21249.0). The line before that should say what authentication method was used. - Authentication via a token will say AuthMethod=SCITOKENS. - Authentication via a proxy will say AuthMethod=GSI.

See the upstream documentation for more details.

Collaboration support

Verify support with collaborations

The tables of collaborations below are updated as frequently as possible. If a collaboration you support is listed as not supporting tokens or WebDav, please contact your collaboration directly to verify that this information is up-to-date.

Pilot job submission

These are the collaborations that support or partially support using tokens for pilot submission:

Collaboration Supports Bearer Tokens
ATLAS Yes
CLAS12 Yes
CMS Yes
EIC Yes
GLOW Yes
GlueX Yes
HCC Yes
IceCube Undergoing testing
LIGO Yes
OSG Yes

Until all of the collaborations you support are using tokens in production, your CE should remain on OSG 3.5, with the 3.5-upcoming repositories enabled.

WebDAV/XRootD File transfer

The following collaborations support support file transfer using WebDAV or XRootD:

Collaboration Supports WebDAV or XRootD
ATLAS Yes
CMS Yes
CLAS12 Yes
EIC N/A
GLOW Yes
GlueX N/A
HCC N/A
IceCube Undergoing testing*
LIGO Undergoing testing*
OSG Yes

* Currently, collaborations testing WebDAV or XRootD support will continue to support other file transfer protocols so it should it should be safe to update your OSG WN clients to OSG 3.6. If you have any questions, please contact your collaboration directly.

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References

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