Author: Harshavardhana <******@****.***>
Date:   Sat Jun 15 11:27:17 2019 -0700

    [security] Match ${aws:username} exactly instead of prefix match (#7791)

    This PR fixes a security issue where an IAM user based
    on his policy is granted more privileges than restricted
    by the users IAM policy.

    This is due to an issue of prefix based Matcher() function
    which was incorrectly matching prefix based on resource

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