feat: optional audiences field on token create

[thyton]

Overview

This PR adds an option to set audiences for the k8s token created from the TokenCreate API

Design of Change

• Add optional token_default_audiences field to the roles path backend
• Add optional audiences field to the credentials path backend
• Add audiences field to the credentials request payload
• Add audiences param to func (c *client) createToken(ctx context.Context, namespace string, name string, ttl time.Duration)

[tvoran]

This looks great! Left a thought about the tests, and I'm also wondering if we've thought about adding this as an option on the role endpoint as well? Something like token_default_audiences, that would be used if the audiences parameter isn't set in the call to the creds endpoint. Similar to how token_default_ttl and ttl are used between the role and creds endpoints.

[tvoran]

I was playing around with this a bit, and noticed that if expectedAudiences is defined as a []interface{} type, then we could do a simpler assert.Equals() here, which would also allow us to check that the default aud is what we expect (https://kubernetes.default.svc.cluster.local).

[thyton]

I had tried assert.Equal() before, and the actual audiences seemed to have a different order each test run. I'm not sure the cause for it

--- FAIL: TestCreds_audiences (0.16s)
    --- FAIL: TestCreds_audiences/default_to_token_default_audiences (0.01s)
        helpers.go:400: 
            	Error Trace:	/Users/thy.ton/go/src/github.com/hashicorp/vault-plugin-secrets-kubernetes/integrationtest/helpers.go:400
            	            				/Users/thy.ton/go/src/github.com/hashicorp/vault-plugin-secrets-kubernetes/integrationtest/creds_integration_test.go:197
            	Error:      	Not equal: 
            	            	expected: []interface {}{"foo", "bar"}
            	            	actual  : []interface {}{"bar", "foo"}
            	            	
            	            	Diff:
            	            	--- Expected
            	            	+++ Actual
            	            	@@ -1,4 +1,4 @@
            	            	 ([]interface {}) (len=2) {
            	            	- (string) (len=3) "foo",
            	            	- (string) (len=3) "bar"
            	            	+ (string) (len=3) "bar",
            	            	+ (string) (len=3) "foo"
            	            	 }
            	Test:       	TestCreds_audiences/default_to_token_default_audiences

[tvoran]

assert.ElementsMatch might work then.

[tvoran]

This is looking good, just a couple suggestions.

[tomhjp]

Looks great! +1 to Theron's suggestions