Fix SSO_START_URL lookup for credential exports (#572)

Use `profile.SSOStartURL()` instead of `profile.AWSConfig.SSOSessionName`
when trying to export credentials. This will fail when the
config does nont have `SSO_START_URL` set on their config.

The `profile.SSOStartURL()` finds it from the session block
which provides the correct URL.

Fix for #571.

pkg/cfaws/cred-exporter.go

@@ -73,7 +73,7 @@ func ExportCredsToProfile(profileName string, creds aws.Credentials) error {
 func ExportAccessTokenToCache(profile *Profile) error {
 	secureSSOTokenStorage := securestorage.NewSecureSSOTokenStorage()
 	// Find the access token for the SSOStartURL and SSOSessionName
-	tokenKey := profile.AWSConfig.SSOStartURL + profile.AWSConfig.SSOSessionName
+	tokenKey := profile.SSOStartURL() + profile.AWSConfig.SSOSessionName
 	cachedToken := secureSSOTokenStorage.GetValidSSOToken(tokenKey)
 	ssoPlainTextOut := CreatePlainTextSSO(profile.AWSConfig, cachedToken)
 	err := ssoPlainTextOut.DumpToCacheDirectory()