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# frozen_string_literal: true
module Atlassian
module JiraConnect
# See documentation about Atlassian asymmetric JWT verification:
# https://developer.atlassian.com/cloud/jira/platform/understanding-jwt-for-connect-apps/#verifying-a-asymmetric-jwt-token-for-install-callbacks
class AsymmetricJwt
include Gitlab::Utils::StrongMemoize
KeyFetchError = Class.new(StandardError)
ALGORITHM = 'RS256'
PUBLIC_KEY_CDN_URL = 'https://connect-install-keys.atlassian.com/'
UUID4_REGEX = /\A[0-9a-f]{8}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{12}\z/.freeze
def initialize(token, verification_claims)
@token = token
@verification_claims = verification_claims
end
def valid?
claims.present? && claims['qsh'] == verification_qsh
end
def iss_claim
return unless claims
claims['iss']
end
private
def claims
strong_memoize(:claims) do
_, jwt_headers = decode_token
public_key = retrieve_public_key(jwt_headers['kid'])
decoded_claims, _ = decode_token(public_key, true, **relevant_claims, verify_aud: true, verify_iss: true, algorithm: ALGORITHM)
decoded_claims
rescue JWT::DecodeError, OpenSSL::PKey::PKeyError, KeyFetchError
end
end
def decode_token(key = nil, verify = false, **claims)
Atlassian::Jwt.decode(@token, key, verify, **claims)
end
def retrieve_public_key(key_id)
raise KeyFetchError unless UUID4_REGEX.match?(key_id)
public_key = Gitlab::HTTP.try_get(PUBLIC_KEY_CDN_URL + key_id).try(:body)
raise KeyFetchError if public_key.blank?
OpenSSL::PKey.read(public_key)
end
def relevant_claims
@verification_claims.slice(:aud, :iss)
end
def verification_qsh
@verification_claims[:qsh]
end
end
end
end
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