132 lines
6.1 KiB
Ruby
132 lines
6.1 KiB
Ruby
# frozen_string_literal: true
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require "cose"
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module DiscourseWebauthn
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class AuthenticationService < BaseValidationService
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##
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# See https://w3c.github.io/webauthn/#sctn-verifying-assertion for
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# the steps followed here. Memoized methods are called in their
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# place in the step flow to make the process clearer.
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def authenticate_security_key
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# Steps 1-5 of this authentication flow are in the frontend at lib/webauthn.js
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if @params.blank? || (!@params.is_a?(Hash) && !@params.is_a?(ActionController::Parameters))
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raise(
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MalformedPublicKeyCredentialError,
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I18n.t("webauthn.validation.malformed_public_key_credential_error"),
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)
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end
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# 6. Identify the user being authenticated and verify that this user is the
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# owner of the public key credential source credentialSource identified by credential.id:
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# 6a. If the user was identified before the authentication ceremony was initiated,
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# verify that the identified user account contains a credential record whose id equals credential.rawId.
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security_key = UserSecurityKey.find_by(credential_id: @params[:credentialId])
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raise(KeyNotFoundError, I18n.t("webauthn.validation.not_found_error")) if security_key.blank?
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if @factor_type == UserSecurityKey.factor_types[:second_factor] &&
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(@current_user == nil || security_key.user == nil || security_key.user != @current_user)
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raise(OwnershipError, I18n.t("webauthn.validation.ownership_error"))
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end
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# 6b. If the user was not identified before the authentication ceremony was initiated,
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# verify that response.userHandle is present. Verify that the user account identified by response.userHandle
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# contains a credential record whose id equals credential.rawId
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if @factor_type == UserSecurityKey.factor_types[:first_factor] &&
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Base64.decode64(@params[:userHandle]) != security_key.user.secure_identifier
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raise(OwnershipError, I18n.t("webauthn.validation.ownership_error"))
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end
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# 7. No upstream step
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# 8. No upstream step
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# 9. Let cData, authData and sig denote the value of credential’s response's clientDataJSON, authenticatorData, and signature respectively.
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# 10. Let JSONtext be the result of running UTF-8 decode on the value of cData.
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# 11. Let C, the client data claimed as used for the signature, be the result of running an implementation-specific JSON parser on JSONtext.
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client_data
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# 12. Verify that the value of C.type is the string webauthn.get.
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validate_webauthn_type(::DiscourseWebauthn::ACCEPTABLE_AUTHENTICATION_TYPE)
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# 13. Verify that the value of C.challenge equals the base64url encoding of options.challenge.
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validate_challenge
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# 14. Verify that the value of C.origin matches the Relying Party's origin.
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validate_origin
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# 15. If C.topOrigin is present:
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# - Verify that the Relying Party expects this credential to be used within an iframe that is not same-origin with its ancestors.
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# - Verify that the value of C.topOrigin matches the origin of a page that the Relying Party expects to be sub-framed within.
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# We are not using this.
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# 16. Verify that the rpIdHash in authData is the SHA-256 hash of the RP ID expected by the Relying Party.
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validate_rp_id_hash
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# 17. Verify that the User Present bit of the flags in authData is set.
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# https://blog.bigbinary.com/2011/07/20/ruby-pack-unpack.html
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#
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validate_user_presence
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#
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# 18. Determine whether user verification is required for this assertion.
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# User verification SHOULD be required if, and only if, options.userVerification is set to required.
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# If user verification was determined to be required, verify that the UV bit of the flags in authData is set.
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# Otherwise, ignore the value of the UV flag.
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validate_user_verification if @factor_type == UserSecurityKey.factor_types[:first_factor]
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# 19. If the BE bit of the flags in authData is not set, verify that the BS bit is not set.
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# Not using this right now.
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# 20. If the credential backup state is used as part of Relying Party business logic or policy...
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# Not using this right now.
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# 21. Verify that the values of the client extension outputs in clientExtensionResults...
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# Not using this right now.
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# 22. Let hash be the result of computing a hash over response.clientDataJSON using SHA-256.
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client_data_hash
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# 23. Using credentialPublicKey, verify that sig is a valid signature over the binary concatenation of authData and hash.
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cose_key = COSE::Key.deserialize(Base64.decode64(security_key.public_key))
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cose_algorithm = COSE::Algorithm.find(cose_key.alg)
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if cose_algorithm.blank?
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Rails.logger.error(
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"Unknown COSE algorithm encountered. alg: #{cose_key.alg}. user_id: #{@current_user.id}. params: #{@params.inspect}",
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)
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raise(UnknownCOSEAlgorithmError, I18n.t("webauthn.validation.unknown_cose_algorithm_error"))
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end
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if !cose_key.to_pkey.verify(
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cose_algorithm.hash_function,
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signature,
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auth_data + client_data_hash,
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)
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raise(PublicKeyError, I18n.t("webauthn.validation.public_key_error"))
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end
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# 24. If authData.signCount is nonzero or credentialRecord.signCount is nonzero...
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# Not using this right now.
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# 25. If response.attestationObject is present and the Relying Party wishes to verify the attestation...
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# Not using this right now.
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# 26. Success! Update the last used at time for the key (credentialRecord).
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security_key.update(last_used: Time.zone.now)
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# Return security key record so controller can use it to update the session
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security_key
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rescue OpenSSL::PKey::PKeyError
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raise(PublicKeyError, I18n.t("webauthn.validation.public_key_error"))
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end
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private
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def auth_data
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@auth_data ||= Base64.decode64(@params[:authenticatorData])
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end
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def signature
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@signature ||= Base64.decode64(@params[:signature])
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end
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end
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end
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