feat(oauth2): Extract actor tokens for cert-bound OAuth2 STS exchange - #13955
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macastelaz wants to merge 6 commits into
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feat(oauth2): Extract actor tokens for cert-bound OAuth2 STS exchange#13955macastelaz wants to merge 6 commits into
macastelaz wants to merge 6 commits into
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Implementation of Phase 1-3 of the Cert-Bound Oauth2 Design Document: 1. Extend IdentityPoolCredentialSource to parse actorTokenFieldName. 2. Relax mutual exclusivity to allow BOTH file and certificate configurations. 3. Parse actor_token_type in ExternalAccountCredentials. 4. Refactor FileIdentityPoolTokenSupplier and track file timestamp via volatile CachedFile for the parsed JSON payload. 5. Inject actor_token and actor_token_type into StsTokenExchangeRequest using ActingParty. 6. Enforce that actor token extraction requires an mTLS STS configuration.
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This pull request introduces support for actor tokens in IdentityPoolCredentials by adding actor token types and field names, introducing the IdentityPoolActorTokenSupplier interface, and refactoring the file-based supplier to FileIdentityPoolTokenSupplier with caching. Feedback suggests optimizing disk I/O by sharing a single FileIdentityPoolTokenSupplier instance for both subject and actor tokens, passing the target field name dynamically, and relaxing the mTLS URL validation check to generically look for .mtls. to support custom universes and Private Service Connect endpoints.
macastelaz
marked this pull request as ready for review
July 30, 2026 17:13
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Background
This PR is the first milestone in supporting Certificate-Bound
OAuth 2.0 Tokens for workloads calling Google APIs via mTLS.
Currently, ExternalAccountCredentials assumes that a workload
provides either a file credential or a certificate configuration,
but not both. For certificate-bound tokens, we need the mTLS
certificate configuration for the transport layer alongside a disk
file containing the JSON payload representing the identity tokens
(e.g., subject and actor tokens).
What this PR does
This PR updates the OAuth2 configuration extraction and STS
(Security Token Service) wire-up to support fetching bound tokens
with delegation.
Specifically, it includes:
Modified IdentityPoolCredentialSource to allow both a
credential_source (file) and a certificate_config (mTLS) to co-
exist without throwing an IllegalArgumentException.
IdentityPoolCredentialSource to parse actor_token_type and
Extended ExternalAccountCredentials and
actor_token_field_name from the JSON configuration payload.
Refactored FileIdentityPoolSubjectTokenSupplier into a generalized
FileIdentityPoolTokenSupplier capable of extracting both actor and
subject tokens. Introduced a volatile cache so that requests for both tokens
during a single refresh cycle do not result in redundant disk I/O.
Updated IdentityPoolCredentials to take in an
IdentityPoolActorTokenSupplier and actorTokenType. Wired these
directly into the StsTokenExchangeRequest using the existing
ActingParty construct so that the actor token gets properly
injected into the STS token exchange payload.
Next Steps
The next phase (which will follow in a separate PR to keep reviews
scoped) will introduce dynamic mTLS transport rotation natively in
GAX and a 401 connection-draining interceptor required for
downstream service retry logic.
Based on design: https://docs.google.com/document/d/1NIKeJX86ETNAjoQA-lZIE_G_8mHspisBaL8gwNCO3dA/edit?resourcekey=0-z7teBZZk0WFIJEHL2ODZxw&tab=t.0