The use of this callback URL for retrieving IAM security credentials has profound security implications:

Now, let's dissect the callback URL: http://169.254.169.254/latest/meta-data/iam/security-credentials/ .

It looks like you posted an encoded URL: callback-url-http-3A-2F-2F169.254.169.254-2Flatest-2Fmeta data-2Fiam-2Fsecurity credentials-2F

: Ensure the IAM role attached to the instance has only the minimum permissions necessary, so stolen credentials have limited impact.