MathieuLoutre/grunt-aws-s3 — pull request #28 by joshuaspence (2014-05-27 22:17:35+00:00)
Title: Support the use of IAM credentials.

When using IAM credentials provided by an EC2 instance, there is no need to explicitly set the `accessKeyId` and `secretAccessKey` properties.

I have tested this on an EC2 instance with IAM access to an S3 bucket. The upload is successful as expected.