hmac_md5

# File lib/net/imap.rb, line 3202
      def hmac_md5(text, key)
        if key.length > 64
          key = Digest::MD5.digest(key)
        end

        k_ipad = key + "\0" * (64 - key.length)
        k_opad = key + "\0" * (64 - key.length)
        for i in 0..63
          k_ipad[i] ^= 0x36
          k_opad[i] ^= 0x5c
        end

        digest = Digest::MD5.digest(k_ipad + text)

        return Digest::MD5.hexdigest(k_opad + digest)
      end