You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: backend.go
    path of file: ./repos/go-ethereum/accounts/external
    
    the code of the file until where you have to start completion: // Copyright 2019 The go-ethereum Authors
// This file is part of the go-ethereum library.
//
// The go-ethereum library is free software: you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later versio
    
func (api *ExternalSigner) SignText(account accounts.Account, text []byte) ([]byte, error) {
	var signature hexutil.Bytes
	var signAddress = common.NewMixedcaseAddress(account.Address)
	if err := api.client.Call(&signature, "account_signData",
		accounts.MimetypeTextPlain,
		&signAddress, // Need to use the pointer here, because of how MarshalJSON is defined
		hexutil.Encode(text)); err != nil {
		return nil, err
	}
	if signature[64] == 27 || signature[64] == 28 {
		// If clef is used as a backend, it may already have transformed
		// the signature to ethereum-type signature.
		signature[64] -= 27 // Transform V from Ethereum-legacy to 0/1
	}
	return signature, nil
}