WebAuthn Library
!
This library is meant to handle Web Authentication for Go apps that wish to implement a multi-factor authentication, passwordless, or usernameless solution for users. This library conforms as much as possible to the guidelines and implementation procedures outlined by the relevant specifications and is conformance tested against the conformance tools.
Go Version Support Policy
This library; unless otherwise explicitly expressed; will officially support the latest minor version of go, and will only offer best effort support for versions of go which are currently supported by the go maintainers (usually 3 minor versions) with a brief transition time (usually 1 patch release of go, for example if go 1.21.0 is released, we will likely still support go 1.17 until go 1.21.1 is released). These specific rules apply at the time of a published release.
This library is intended to be used with Go Toolchains as indicated by the
toolchain directive in the go.mod.
This library in our opinion handles a critical element of security in a dependent project and we aim to avoid backwards compatibility at the cost of security wherever possible. We also consider this especially important in a language like go where their backwards compatibility when upgrading the compile tools is usually flawless.
This policy means that users who wish to build this with older versions of go may find there are features being used which are not available in that version. The current intentionally supported versions of go are as follows:
- go 1.27
- go 1.26
- ~~go 1.25~~
Status
This library is still version 0, as per Semantic Versioning 2.0 rules there may be breaking changes without warning. While we strive to avoid such changes and strive to notify users they may be unavoidable.
Quickstart
First run go get github.com/go-webauthn/webauthn and initialize it in your application with basic configuration
values.
Make sure your user model is able to handle the interface functions laid out in the
webauthn.User interface. This means also
supporting the storage and retrieval of the [webauthn.Credential] struct which can be encoded fairly easily.
Notable Changes
The notable breaking changes made by this library are documented in the release notes. If a substantial breaking change occurs that is expected to be difficult to adapt to it may also be noted in the Migration Guide.
Examples
The examples are documented in the [go docs -> webauthn -> examples].
Documentation
The intent is to move all documentation into the [go docs], and a good starting place is the [go docs -> webauthn] location.
Credential Record
_Important:_ It is considered critical that implementers carefully read the [webauthn.Credential] struct documentation as part of the implementation process.
The WebAuthn Level 3 specification describes the Credential Record which includes several recommended and optional elements that you should store. See § 4 Terminology for details.
Most Credential Record members have a corresponding field in the [webauthn.Credential] struct. Two do not, and are
noted as such in the table below: type is a constant for WebAuthn, and rpId is scoping information you must store
yourself. The struct additionally carries several fields with no Credential Record counterpart. Mappings are given
for both encodings the struct supports, so the values can be stored as JSON or as MessagePack rather than as columns.
Nested fields are written with a dot (i.e. attestation.object is the object member of the attestation object).
| Specification Field | Library Field | JSON Field | MessagePack Field | Notes |
|:-------------------------:|:--------------------------:|:--------------------------:|:-----------------:|:------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------:|
| type | N/A | N/A | N/A | Always public-key for WebAuthn. |
| id | ID | id | id | |
| publicKey | PublicKey | publicKey | pk | |
| signCount | Authenticator.SignCount | authenticator.signCount | a.sc | Write back on every successful login. |
| transports | Transport | transport | t | |
| uvInitialized | Flags.UserVerified | flags.userVerified | flg | MessagePack packs every flag into the single flg octet. Write back on every successful login. |
| backupEligible | Flags.BackupEligible | flags.backupEligible | flg | Packed into flg as above. |
| backupState | Flags.BackupState | flags.backupState | flg | Packed into flg as above. Write back on every successful login when backupEligible is true. |
| attestationObject | Attestation.Object | attestation.object | att.obj | OPTIONAL in the specification; required by [Credential Verify]. |
| attestationClientDataJSON | Attestation.ClientDataJSON | attestation.clientDataJSON | att.cdj | OPTIONAL in the specification; required by [Credential Verify]. |
| rpId | N/A | N/A | N/A | OPTIONAL in the specification. Not a field of the struct. Store it as a column of your own; credentials MUST be partitioned by Relying Party ID. |
| N/A | AttestationType | attestationType | atttype | The attestation type conveyed by the authenticator (i.e. basic_full, basic_surrogate). Records that predate the split from the format are migrated by the custom Credential.UnmarshalJSON. |
| N/A | AttestationFormat | attestationFormat | attfmt | The attestation statement format identifier (i.e. packed, tpm). Not a Credential Record member at Level 3. |
| N/A | Attestation | attestation | att | A composite object holding the two OPTIONAL Credential Record members above plus additional values used to validate this Credential. |
| N/A | Extensions | extensions | ext | The durable extension results of the registration ceremony. Added in v0.18.0; see the Migration Guide. |
| N/A | Authenticator | authenticator | a | A composite object holding the AAGUID, sign count, clone warning, and attachment. |
For the recommended schema shape, which fields must be written back on every successful FinishLogin /
ValidateLogin, and how to store the Relying Party ID and User Handle, see the [Storage] section of the package
documentation.
Flags
It's important to note that the recommendations and requirements for flag storage have changed over the course of the evolution of the WebAuthn specification. We at the present time only make the flags classified like this available for easy storage however we also make the Protocol Value available. At such a time as these recommendations or requirements change we will adapt accordingly. The Protocol Value is a raw representation of the flags and as such is resistant to breaking changes whereas the other flags or lack thereof may not be.
Implementers are therefore encouraged to use func (CredentialFlags) ProtocolValue to retrieve the raw value and webauthn.NewCredentialFlags to restore it; and instead of using the individual flags to store the value store the Protocol Value, and only store the individual flags as a means to perform compliance related decisions.
Storage
It is also important to note that restoring the [webauthn.Credential] with the correct values will likely affect the validity of the [webauthn.Credential], i.e. if some values are not restored the [webauthn.Credential] may fail validation in this scenario.
Verification
As long as the [webauthn.Credential] struct has exactly the same values when restored the [Credential Verify] function
can be used to verify the credential against the [metadata.Provider]. It also takes the protocol.AttestationPolicy
and protocol.SignaturePolicy values the ceremony was performed under, which are carried by the
webauthn.Config Attestation and Signature
fields. This can be either done during registration, on every login, or with an audit schedule.
In addition to using the [Credential Verify] function the webauthn.Config can contain a provider which will process all registrations automatically.
At this time no tooling exists to verify the credential automatically outside the registration flow. Implementation of this is considered domain logic and beyond the scope of what we provide documentation for; we just provide the necessary tooling to implement this yourself.
Support
This section indicates various support statuses for specific elements of the spec. The level column indicates the spec level this library currently supports for that statement format by the first number, and the number in parenthesis represents when the format was introduced into the spec.
Attestation Format
| Format | Identifier | Supported | Level |
|:-------------------------------------------------------------------------------------------------------------------------:|:-------------------:|:---------:|:-----:|
| §8.2 Packed Attestation Statement Format | packed | Yes | 3 (1) |
| §8.3 TPM Attestation Statement Format | tpm | Yes | 3 (1) |
| §8.4 Android Key Attestation Statement Format | android-key | Yes | 3 (1) |
| §8.5 Android SafetyNet Attestation Statement Format | android-safetynet | Yes | 3 (1) |
| §8.6 FIDO U2F Attestation Statement Format | fido-u2f | Yes | 3 (1) |
| §8.7 None Attestation Statement Format | none | Yes | 3 (1) |
| §8.8 Apple Anonymous Attestation Statement Format | apple | Yes | 3 (2) |
| §8.9 Compound Attestation Statement Format | compound | Yes | 3 (3) |
Extensions
Extensions with a typed input have a dedicated functional option (webauthn.WithExtension) taking typed
Go values, applied via webauthn.WithExtensions (registration) or webauthn.WithAssertionExtensions
(authentication); a typed client output is exposed as a field of protocol.AuthenticationExtensionsClientOutputs,
and a typed authenticator output as a field of protocol.AuthenticatorExtensionOutputs. An identifier with no
dedicated option is not modelled: it can still be set on input with the generic webauthn.WithExtension, which
conveys the value to the client verbatim, and any output returned under that identifier is preserved in the
relevant Extra map rather than dropped.
Standardized and Specification Listed Extensions:
| Extension | Identifier | Registration | Authentication | Level |
|:-------------------------------------------------------------------------------------------------------------------------------:|:--------------:|:---------------------------------------------:|:-----------------------------------------------------------------------------:|:-----:|
| §10.1.1 FIDO AppID Extension | appid | N/A[^2] | WithExtensionAppID | 3 (1) |
| §10.1.2 FIDO AppID Exclusion Extension | appidExclude | WithExtensionAppIDExclude | N/A[^1] | 3 (1) |
| §10.1.3 Credential Properties Extension | credProps | WithExtensionCredProps | N/A[^1] | 3 (2) |
| §10.1.4 Pseudo-Random Function Extension | prf | WithExtensionPRF, WithExtensionPRFSupport | WithExtensionPRF, WithExtensionPRFSupport, WithExtensionPRFByCredential | 3 (2) |
| §10.1.5 Large Blob Storage Extension | largeBlob | WithExtensionLargeBlobSupport | WithExtensionLargeBlobRead, WithExtensionLargeBlobWrite | 3 (2) |
CTAP 2.1 / CTAP 2.2 / CTAP 2.3 Extensions registered in the IANA "WebAuthn Extension Identifiers" registry:
| Extension | Identifier | Registration | Authentication |
|:-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------:|:------------------------------------:|:-----------------------------------------:|:----------------------------:|
| Credential Protection Extension | credProtect | WithExtensionCredentialProtectionPolicy | N/A[^1] |
| Credential Blob Extension | credBlob / getCredBlob | WithExtensionCredBlob | WithExtensionGetCredBlob |
| Minimum PIN Length Extension | minPinLength | WithExtensionMinPinLength | N/A[^1] |
| HMAC Secret Extension | hmacCreateSecret / hmacGetSecret | WithExtensionHMACCreateSecret | WithExtensionHMACGetSecret |
| User Verification Method Extension[^5] | uvm | WithExtensionUVM | WithExtensionUVM |
| Large Blob Key Extension | largeBlobKey | Not modelled[^3] | Not modelled[^3] |
| PIN Complexity Extension | pinComplexityPolicy | Not modelled[^4] | N/A[^1] |
| HMAC Secret MakeCredential Extension | hmac-secret-mc | Not modelled[^4] | N/A[^1] |
| Third-Party Payment Authentication Extension | thirdPartyPayment | Not modelled[^4] | Not modelled[^4] |
The CTAP authenticator data also carries a hmac-secret extension output identifier (protocol.ExtensionHMACSecret),
distinct from the hmacCreateSecret / hmacGetSecret client-facing identifiers above; it is decoded automatically
into AuthenticatorExtensionOutputs.HMACSecret / HMACSecretOutput and is not something a Relying Party requests.
[^1]: This extension is only applicable during Registration.
[^2]: This extension is only applicable during Authentication.
[^3]: Deliberately not modelled. CTAP 2.3 §12.3 defines no client extension input, output, or processing for
largeBlobKey: it is a CTAP response member returned directly to the platform, not to the Relying Party.
protocol.ExtensionLargeBlobKey is kept as a documented identifier and remains reachable verbatim via
webauthn.WithExtension.
[^4]: Not modelled. Set on input with webauthn.WithExtension; an output returned under this identifier is
preserved in the outputs' Extra map.
[^5]: uvm was deprecated from the core WebAuthn spec text at Level 3 (see the deprecated extensions table
below) but remains registered as a CTAP 2.1/2.2/2.3 extension in the IANA registry and is still forwarded by
several clients, hence a dedicated option.
Extensions that have been deprecated and removed from the spec. The deprecated level is the first spec level that did
not include the extension. These are all technically reachable as untyped values via webauthn.WithExtension, but
have no official (typed) support from this library, and are most likely not supported by either browsers or
authenticators. The one exception is uvm: it remains registered as a CTAP extension and is modelled, so
webauthn.WithExtension rejects it and webauthn.WithExtensionUVM is used instead.
These extensions often either were excluded due to privacy or security concerns, were introduced into the core of the spec as legitimate inputs outside of extensions, or never received support from browsers or authenticators.
| Format | Identifier | Level (Added) | Level (Deprecated) |
|:-----------------------------------------------------------------------------------------------------------------------------------------:|:---------------------:|:-------------:|:------------------:|
| Generic Transaction Authorization Extension | txAuthGeneric | 1 | 2 |
| Authenticator Selection Extension | authnSel | 1 | 2 |
| Supported Extensions Extension | exts | 1 | 2 |
| User Verification Index Extension | uvi | 1 | 2 |
| Location Extension | loc | 1 | 2 |
| User Verification Method Extension | uvm | 1 | 3 |
| Biometric Authenticator Performance Bounds Extension | biometricPerfBounds | 1 | 2 |
Acknowledgements
We graciously acknowledge the original authors of this library [github.com/duo-labs/webauthn] for their amazing implementation. In particular we'd like to acknowledge Nick Steele who not only created the original library, but maintained it, and has been an active member of the WebAuthn Working Group quite some time. Without their amazing work this library could not exist.
[github.com/duo-labs/webauthn]: https://github.com/duo-labs/webauthn [webauthn.Credential]: https://pkg.go.dev/github.com/go-webauthn/webauthn/webauthn#Credential [metadata.Provider]: https://pkg.go.dev/github.com/go-webauthn/webauthn/metadata#Provider [Credential Verify]: https://pkg.go.dev/github.com/go-webauthn/webauthn/webauthn#Credential.Verify [Storage]: https://pkg.go.dev/github.com/go-webauthn/webauthn/webauthn#hdr-Storage
[go docs]: https://pkg.go.dev/github.com/go-webauthn/webauthn
[go docs -> webauthn]: https://pkg.go.dev/github.com/go-webauthn/webauthn/webauthn
[go docs -> webauthn -> examples]: https://pkg.go.dev/github.com/go-webauthn/webauthn/webauthn#pkg-examples