Fix role authentication to use the session token correctly

[uduncanu]

Authenticating using an IAM role currently gives this error:

AttributeError: 'datetime.datetime' object has no attribute 'split'

That's due to us passing a datetime object through instead of what should be a string containing the session token.

Switching to using the SessionToken value instead makes it complete as expected.

[ross]

Interesting. Surprised this worked in the past. Maybe AWS changed the SessionToken's value/behavior and it used to be the same as the expiration.

Anyway, been thinking about looking at what and AWS secrets handler would look like which could deal with all these sorts of things in an more centralized/focused way rather than having to include code/support in all of the providers & sources for it. If/when that happens this stuff may get deprecated in favor of that route.

/cc octodns/octodns#1140 for the secrets handler functionality

[ross]

Looks like a unit test is failing now. Probably needs a tweak to the mock/setup. ./script/coverage should run everything locally. May require a one-time ./script/bootstrap first.

[sssss15]

Hi All,
I am also getting this error while adding role_arn inside route53 provider,
Is there any workaround for this.

[ross]

/cc #88