Typescript: Missing Type (Buffer) for SSL Configuration (key, cert. ca) for 'ConnectionOptions' type

[happyoka]

Describe the bug
Type 'Buffer' is not assignable to type 'string'.ts(2322)
connection.d.ts(199, 3): The expected type comes from property 'key' which is declared here on type 'ConnectionOptions'

To Reproduce
Steps to reproduce the behavior:

const connectionOptions : ConnectionOptions = {
    host: '192.168.80.90',
    port: 5671,
    transport: 'tls',
    servername: 'root',
    reconnect: true,
    key: fs.readFileSync(path.resolve(__dirname,'../client.key')),
    cert: fs.readFileSync(path.resolve(__dirname,'../client-cert.pem')),
    ca: fs.readFileSync(path.resolve(__dirname,'../server.pem')),
    rejectUnauthorized: false
 };

Expected behavior
No Linting error or typescript error

Package-version: 2.1.0
node.js version: v16.14.0
OS name and version: Window

Additional context
Add any other context about the problem here.