The Cloud SQL Auth proxy is the recommended method for connecting to Cloud SQL, as it provides secure access to your instances without the need for Authorized networks or for configuring SSL. While Cloud Identity is an Identity as a Service (IDaaS) solution, and IAM manages identities and their permissions, neither are specifically recommended for Cloud SQL authentication. Strong encryption protects data confidentiality and integrity but does not serve as an authentication method. For more details, refer to Google Cloud's documentation.