fix: saml order of principal and role mixed

[Timboo89]

Hi there,

I was just writing a saml plugin, realizing that it always came to issues because of the order between role arn and principal arn. Fixes:

1. In the saml response, you get the arns like this: "role-arn,principal-arn" [1] You had it correct once and once and than once the other way around.
2. Parsing the actual role arn and principal arn from the saml response was also in the wrong order here and here

In case (1) differs from response to response I'd be glad to write a less static check here.

[1] At least this is how the response looked like I was receiving.