Create an IAM user that has only programmatic access. Create a new access key pair. Add environmental variables to the Lambda function with the access key ID and secret access key. Modify the Lambda function to use the environmental variables at run time during communication with Amazon S3.

Generate an Amazon EC2 key pair. Store the private key in AWS Secrets Manager. Modify the Lambda function to retrieve the private key from Secrets Manager and to use the private key during communication with Amazon S3.

Create an IAM role for the Lambda function. Attach an IAM policy that allows access to the S3 bucket.

Create an IAM role for the Lambda function. Attach a bucket policy to the S3 bucket to allow access. Specify the function's IAM role as the principal.

Create a security group. Attach the security group to the Lambda function. Attach a bucket policy that allows access to the S3 bucket through the security group ID.