Fixes for okta + govcloud

[duckfez]

Fixes #475.

Added the known SAML signin pages for the AWS GovCloud (US) and AWS China into the okta provider, as well as into the SAML assertion parser.

Note this may not be good, idiomatic golang... Sorry, my first attempt at doing something with it.

[missingcharacter]

@duckfez does this branch fails govcloud and AWS China for you too? #469

[duckfez]

@missingcharacter I can't test AWS China, don't have an account there. When I started working on getting GovCloud (US) to work, I first fixed pkg/provider/okta/okta.go to add the GovCloud SAML URL there. Then, I ran into the problem in aws_account.go and saw the master branch already had been worked on for AWS China. So, I went back and added the AWS China URL into the okta provider as well.

[missingcharacter]

@duckfez than maybe a better question is: do your changes to pkg/provider/okta/okta.go play well with #469 ?

[duckfez]

@missingcharacter Based on my limited understanding of the code base - I think your changes in #469 in aws_account.go are likely superior to my own and should replace them. But, even with what you've done, my changes to the Okta provider are still necessary.

[missingcharacter]

@duckfez I agree your okta changes are necessary, what I'm wondering is if both changes work together.

[duckfez]

I'll merge #469 into what I have here and give it a try to see.

[duckfez]

@missingcharacter I merged your branch with mine and fixed the small merge conflicts in aws_account.go. Very first test I get one of the errors that was reporting in #469:

Failed to assume role, please check whether you are permitted to assume the given role for the AWS service: error parsing aws role accounts: error retrieving AWS login form: Post "urn:amazon:webservices": unsupported protocol scheme "urn"

I'll work on trying to debug it and report back if I come up with anything.

[duckfez]

Modified this to be dependent on (and avoid merge conflicts with) #481.