code: def encode_signature(sig_r, sig_s):
      
      # enforce low-s 
      if sig_s * 2 >= SECP256k1_order:
          log.debug("High-S to low-S")
          sig_s = SECP256k1_order - sig_s
  
      sig_bin = '{:064x}{:064x}'.format(sig_r, sig_s).decode('hex')
      assert len(sig_bin) == 64
  
      sig_b64 = base64.b64encode(sig_bin)
      return sig_b64
docs: Encode an ECDSA signature, with low-s