Why did the reformers include the book of Hebrews in the canon?

Related: [Why was Hebrews included in the canon?](https://christianity.stackexchange.com/q/6557/21576) It's widely known that Hebrews has been in the canon of most of Christendom for a long time, originally on the basis of Pauline authorship (see the linked answer above for more). Despite some divergence of opinion (cf. [Martin Luther](https://en.wikipedia.org/wiki/Luther_Bible#View_of_canonicity)) , most of the reformers considered it canonical as well. Here, I'd like to understand their reasons – that is: Why did significant reformers (e.g., [John Calvin](https://en.wikipedia.org/wiki/John_Calvin) , [John Knox](https://en.wikipedia.org/wiki/John_Knox) , [Ulrich Zwingli](https://en.wikipedia.org/wiki/Huldrych_Zwingli)) generally include Hebrews in the canon? - Did they still believe that Paul wrote the book, and thus include it on the basis of apostolic authorship? - Or did they accept it based on other factors, like the testimony of the early church, perhaps because Pauline authorship had already begun to be doubted?