Add Result types to Go SDK and properly populate body/map fields (#358)

api/authmethods/authenticate.go

@@ -8,7 +8,7 @@ import (
 	"github.com/hashicorp/boundary/api/authtokens"
 )
 
-func (c *Client) Authenticate(ctx context.Context, authMethodId string, credentials map[string]interface{}, opt ...Option) (*authtokens.AuthToken, *api.Error, error) {
+func (c *Client) Authenticate(ctx context.Context, authMethodId string, credentials map[string]interface{}, opt ...Option) (*authtokens.AuthTokenReadResult, *api.Error, error) {
 	if c.client == nil {
 		return nil, nil, fmt.Errorf("nil client in Authenticate request")
 	}
@@ -29,8 +29,9 @@ func (c *Client) Authenticate(ctx context.Context, authMethodId string, credenti
 		return nil, nil, fmt.Errorf("error performing client request during Authenticate call: %w", err)
 	}
 
-	target := new(authtokens.AuthToken)
-	apiErr, err := resp.Decode(target)
+	target := new(authtokens.AuthTokenReadResult)
+	target.Item = new(authtokens.AuthToken)
+	apiErr, err := resp.Decode(target.Item)
 	if err != nil {
 		return nil, nil, fmt.Errorf("error decoding Authenticate response: %w", err)
 	}