I have not seen an article questioning it’s authenticity, I have seen Perry campaign statements saying it fell short of endorsing Hillarycare.
Timeline is important. The letter is dated two months after the inauguration, 6 months before Hillary testified before congress and 8 months before legislation was introduced.
It's a conscientious elected official writing on behalf of his constituents as Hillary embarked on her healthcare reform task force.
Spinning it as support for what Hillary ultimately came up with is a lie of epic proportions.