AWS Lambda: How to store secret to external API?

I need your help on this question. I'm currently building a monitoring tool based on AWS Lambda. Given a set of metrics, the Lambdas should be able to send SMS using Twilio API. To be able to use the API, Twilio provide an account SID and an auth token.

My question is the following: "How and where should I store these secrets?"

I'm currently thinking to use AWS KMS but there might be other better solutions. What do you think?

Thanks a lot for your time and your answers.

Best regards, Jonathan.