class Slack::Events::Request

def body

Request body. 
def body
  @body ||= begin
    body = http_request.body.read
    http_request.body.rewind
    body
  end
end

def expired?

Returns true if the signature coming from Slack has expired. 
def expired?
  timestamp.nil? || (Time.now.to_i - timestamp.to_i).abs > signature_expires_in
end

def initialize(http_request, options = {}) 

def initialize(http_request, options = {})
  @http_request = http_request
  @signing_secret = options[:signing_secret] || Slack::Events.config.signing_secret
  @signature_expires_in =
    options[:signature_expires_in] || Slack::Events.config.signature_expires_in
end

def signature

Slack is sending using a standard HMAC-SHA256 keyed hash.
The signature is created by combining the signing secret with the body of the request 
def signature
  @signature ||= http_request.get_header('HTTP_X_SLACK_SIGNATURE')
end

def timestamp

Request timestamp. 
def timestamp
  @timestamp ||= http_request.get_header('HTTP_X_SLACK_REQUEST_TIMESTAMP')
end

def valid?

Returns true if the signature coming from Slack is valid. 
def valid?
  raise MissingSigningSecret unless signing_secret
  digest = OpenSSL::Digest::SHA256.new
  signature_basestring = [version, timestamp, body].join(':')
  hex_hash = OpenSSL::HMAC.hexdigest(digest, signing_secret, signature_basestring)
  computed_signature = [version, hex_hash].join('=')
  computed_signature == signature
end

def verify!

Validates the request signature and its expiration. 
def verify!
  raise TimestampExpired if expired?
  raise InvalidSignature unless valid?
  true
end

def version

Signature version. 
def version
  'v0'
end