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package protocol
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import (
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"crypto/subtle"
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"fmt"
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"net/url"
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"strings"
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)
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// CollectedClientData represents the contextual bindings of both the WebAuthn Relying Party
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// and the client. It is a key-value mapping whose keys are strings. Values can be any type
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// that has a valid encoding in JSON. Its structure is defined by the following Web IDL.
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//
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// Specification: §5.8.1. Client Data Used in WebAuthn Signatures (https://www.w3.org/TR/webauthn/#dictdef-collectedclientdata)
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type CollectedClientData struct {
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// Type contains the string "webauthn.create" when creating new credentials, and "webauthn.get" when getting an
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// assertion from an existing credential. The purpose of this member is to prevent certain types of signature
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// confusion attacks (where an attacker substitutes one legitimate signature for another).
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Type CeremonyType `json:"type"`
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// Challenge contains the base64url encoding of the challenge provided by the Relying Party.
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Challenge string `json:"challenge"`
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// Origin contains the fully qualified origin of the requester, as provided to the authenticator by the client.
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Origin string `json:"origin"`
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// TopOrigin contains the fully qualified top-level origin of the requester when the client is cross-origin.
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// This is only present when CrossOrigin is true.
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//
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// WebAuthn Level 3.
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TopOrigin string `json:"topOrigin,omitempty"`
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// CrossOrigin indicates whether the calling context is an iframe that is not same-origin with its ancestor.
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//
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// WebAuthn Level 3.
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CrossOrigin bool `json:"crossOrigin,omitempty"`
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// TokenBinding contains information about the state of the Token Binding protocol.
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TokenBinding *TokenBinding `json:"tokenBinding,omitempty"`
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// Hint is an opaque field that may be added by the client. Chromium-based browsers include this field to remind
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// implementers not to perform string comparison on the clientDataJSON.
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Hint string `json:"new_keys_may_be_added_here,omitempty"`
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}
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// CeremonyType represents the type of WebAuthn ceremony being performed.
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//
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// Specification: §5.8.1. Client Data Used in WebAuthn Signatures (https://www.w3.org/TR/webauthn/#dom-collectedclientdata-type)
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type CeremonyType string
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const (
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// CreateCeremony is the ceremony type for credential registration ("webauthn.create").
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CreateCeremony CeremonyType = "webauthn.create"
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// AssertCeremony is the ceremony type for authentication assertion ("webauthn.get").
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AssertCeremony CeremonyType = "webauthn.get"
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)
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// TokenBinding contains information about the state of the Token Binding protocol used when communicating with the
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// Relying Party. Its absence indicates that the client doesn't support token binding.
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//
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// Specification: §5.8.1. Client Data Used in WebAuthn Signatures (https://www.w3.org/TR/webauthn/#dom-collectedclientdata-tokenbinding)
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type TokenBinding struct {
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Status TokenBindingStatus `json:"status"`
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ID string `json:"id,omitempty"`
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}
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// TokenBindingStatus represents the state of Token Binding between the client and the Relying Party.
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type TokenBindingStatus string
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const (
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// Present indicates token binding was used when communicating with the
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// Relying Party. In this case, the id member MUST be present.
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Present TokenBindingStatus = "present"
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// Supported indicates the client supports token binding, but it was not
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// negotiated when communicating with the Relying Party.
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Supported TokenBindingStatus = "supported"
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// NotSupported indicates token binding not supported
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// when communicating with the Relying Party.
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NotSupported TokenBindingStatus = "not-supported"
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)
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// FullyQualifiedOrigin returns the origin per the HTML spec: (scheme)://(host)[:(port)].
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func FullyQualifiedOrigin(rawOrigin string) (fqOrigin string, err error) {
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if strings.HasPrefix(rawOrigin, "android:apk-key-hash:") {
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return rawOrigin, nil
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}
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var origin *url.URL
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if origin, err = url.ParseRequestURI(rawOrigin); err != nil {
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return "", err
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}
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if origin.Host == "" {
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return "", fmt.Errorf("url '%s' does not have a host", rawOrigin)
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}
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origin.Path, origin.RawPath, origin.RawQuery, origin.User = "", "", "", nil
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return origin.String(), nil
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}
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// Verify handles steps 3 through 6 of verifying the registering client data of a
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// new credential and steps 7 through 10 of verifying an authentication assertion
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// See https://www.w3.org/TR/webauthn/#registering-a-new-credential
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// and https://www.w3.org/TR/webauthn/#verifying-assertion
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//
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// Note: the rpTopOriginsVerify parameter does not accept the TopOriginVerificationMode value of
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// TopOriginDefaultVerificationMode as it's expected this value is updated by the config validation process.
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//
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//nolint:gocyclo
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func (c *CollectedClientData) Verify(storedChallenge string, ceremony CeremonyType, rpOrigins, rpTopOrigins []string, rpTopOriginsVerify TopOriginVerificationMode, allowCrossOrigin bool) (err error) {
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// Registration Step 3. Verify that the value of C.type is webauthn.create.
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// Assertion Step 7. Verify that the value of C.type is the string webauthn.get.
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if c.Type != ceremony {
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return ErrVerification.WithDetails("Error validating ceremony type").WithInfo(fmt.Sprintf("Expected Value: %s, Received: %s", ceremony, c.Type))
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}
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// Registration Step 4. Verify that the value of C.challenge matches the challenge
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// that was sent to the authenticator in the create() call.
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// Assertion Step 8. Verify that the value of C.challenge matches the challenge
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// that was sent to the authenticator in the PublicKeyCredentialRequestOptions
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// passed to the get() call.
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challenge := c.Challenge
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if subtle.ConstantTimeCompare([]byte(storedChallenge), []byte(challenge)) != 1 {
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return ErrVerification.
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WithDetails("Error validating challenge").
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WithInfo(fmt.Sprintf("Expected b Value: %#v\nReceived b: %#v\n", storedChallenge, challenge))
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}
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// Registration Step 5 & Assertion Step 9. Verify that the value of C.origin matches
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// the Relying Party's origin.
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if !IsOriginInHaystack(c.Origin, rpOrigins) {
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return ErrVerification.
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WithDetails("Error validating origin").
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WithInfo(fmt.Sprintf("Expected Values: %s, Received: %s", rpOrigins, c.Origin))
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}
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if !allowCrossOrigin && c.CrossOrigin {
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return ErrVerification.
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WithDetails("Error validating cross origin flag").
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WithInfo("The cross origin flag is invalid due to the configuration.")
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}
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switch len(c.TopOrigin) {
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case 0:
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break
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default:
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if !c.CrossOrigin {
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return ErrVerification.
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WithDetails("Error validating topOrigin").
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WithInfo("The topOrigin can't have values unless crossOrigin is true.")
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}
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var possibleTopOrigins []string
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switch rpTopOriginsVerify {
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case TopOriginExplicitVerificationMode:
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possibleTopOrigins = rpTopOrigins
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case TopOriginAutoVerificationMode:
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possibleTopOrigins = make([]string, 0, len(rpTopOrigins)+len(rpOrigins))
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possibleTopOrigins = append(possibleTopOrigins, rpTopOrigins...)
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possibleTopOrigins = append(possibleTopOrigins, rpOrigins...)
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case TopOriginImplicitVerificationMode:
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possibleTopOrigins = rpOrigins
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default:
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return ErrNotImplemented.WithDetails("Error handling unknown Top Origin verification mode")
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}
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if !IsOriginInHaystack(c.TopOrigin, possibleTopOrigins) {
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return ErrVerification.
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WithDetails("Error validating top origin").
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WithInfo(fmt.Sprintf("Expected Values: %s, Received: %s", possibleTopOrigins, c.TopOrigin))
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}
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}
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// Registration Step 6 and Assertion Step 10. Verify that the value of C.tokenBinding.status
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// matches the state of Token Binding for the TLS connection over which the assertion was
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// obtained. If Token Binding was used on that TLS connection, also verify that C.tokenBinding.id
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// matches the base64url encoding of the Token Binding ID for the connection.
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if c.TokenBinding != nil {
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if c.TokenBinding.Status == "" {
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return ErrParsingData.WithDetails("Error decoding clientData, token binding present without status")
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}
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if c.TokenBinding.Status != Present && c.TokenBinding.Status != Supported && c.TokenBinding.Status != NotSupported {
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return ErrParsingData.
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WithDetails("Error decoding clientData, token binding present with invalid status").
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WithInfo(fmt.Sprintf("Got: %s", c.TokenBinding.Status))
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}
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}
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// Not yet fully implemented by the spec, browsers, and me.
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return nil
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}
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// TopOriginVerificationMode determines how the Relying Party validates the topOrigin field in
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// [CollectedClientData]. This is relevant for cross-origin iframe scenarios where the top-level browsing context's
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// origin differs from the embedded origin making the WebAuthn API call.
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//
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// WebAuthn Level 3.
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type TopOriginVerificationMode int
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const (
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// TopOriginDefaultVerificationMode is the zero value of [TopOriginVerificationMode] and has no matching rule in
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// the verifier; passing it directly to [CollectedClientData.Verify] returns an "unknown Top Origin verification
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// mode" error. High-level callers using [webauthn.Config] have this value coerced to
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// [TopOriginExplicitVerificationMode] by config validation, which is the recommended default.
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TopOriginDefaultVerificationMode TopOriginVerificationMode = iota
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// TopOriginAutoVerificationMode accepts the Top Origin if it matches any entry in either the allowed Top Origins
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// list or the allowed Origins list. The two lists are unioned (RPTopOrigins ∪ RPOrigins). This is the most
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// permissive of the three active modes and should only be used when an RP deliberately wants cross-origin and
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// same-origin embeddings to share an allow-list.
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TopOriginAutoVerificationMode
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// TopOriginImplicitVerificationMode accepts the Top Origin only if it matches an entry in the allowed Origins
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// list (RPOrigins). The RPTopOrigins list is ignored in this mode.
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TopOriginImplicitVerificationMode
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// TopOriginExplicitVerificationMode accepts the Top Origin only if it matches an entry in the allowed Top Origins
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// list (RPTopOrigins). The RPOrigins list is ignored in this mode. This is the strictest mode and the one
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// [webauthn.Config] coerces the zero value to.
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TopOriginExplicitVerificationMode
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)
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// IsOriginInHaystack checks if the needle is in the haystack using the mechanism to determine origin equality defined
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// in HTML5 Section 5.3 and RFC3986 Section 6.2.1.
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//
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// Specifically if the needle value has the 'http://' or 'https://' prefix (case-insensitive) and can be parsed as a
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// URL; we check each item in the haystack to see if it matches the same rules, and then if the scheme and host (with
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// a normalized port) components match case-insensitively then they're considered a match.
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//
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// If the needle value does not have the 'http://' or 'https://' prefix (case-insensitive) or can't be parsed as a URL
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// equality is determined using simple string comparison.
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//
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// It is important to note that this function completely ignores Apple Associated Domains entirely as Apple is using
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// an unassigned Well-Known URI in breech of Well-Known Uniform Resource Identifiers (RFC8615).
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//
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// See (Origin Definition): https://www.w3.org/TR/2011/WD-html5-20110525/origin-0.html
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//
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// See (Simple String Comparison Definition): https://datatracker.ietf.org/doc/html/rfc3986#section-6.2.1
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//
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// See (Apple Associated Domains): https://developer.apple.com/documentation/xcode/supporting-associated-domains
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//
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// See (IANA Well Known URI Assignments): https://www.iana.org/assignments/well-known-uris/well-known-uris.xhtml
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//
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// See (Well-Known Uniform Resource Identifiers): https://datatracker.ietf.org/doc/html/rfc8615
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func IsOriginInHaystack(needle string, haystack []string) bool {
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needleURI := parseOriginURI(needle)
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if needleURI != nil {
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for _, hay := range haystack {
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if hayURI := parseOriginURI(hay); hayURI != nil {
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if isOriginEqual(needleURI, hayURI) {
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return true
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}
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}
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}
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} else {
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for _, hay := range haystack {
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if needle == hay {
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return true
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}
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}
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}
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return false
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}
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func isOriginEqual(a *url.URL, b *url.URL) bool {
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if !strings.EqualFold(a.Scheme, b.Scheme) {
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return false
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}
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if !strings.EqualFold(a.Host, b.Host) {
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return false
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}
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return true
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}
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func parseOriginURI(raw string) *url.URL {
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if !isPossibleFQDN(raw) {
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return nil
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}
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// We can ignore the error here because it's effectively not a FQDN if this fails.
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uri, _ := url.Parse(raw)
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if uri == nil {
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return nil
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}
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// Normalize the port if necessary.
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switch uri.Scheme {
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case "http":
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if uri.Port() == "80" {
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uri.Host = uri.Hostname()
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}
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case "https":
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if uri.Port() == "443" {
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uri.Host = uri.Hostname()
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}
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}
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return uri
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}
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func isPossibleFQDN(raw string) bool {
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normalized := strings.ToLower(raw)
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return strings.HasPrefix(normalized, "http://") || strings.HasPrefix(normalized, "https://")
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}
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