Remove use of Privileged Credentials (#535)

- Leverage on MinIO Oauth integration instead of the 
  current Console implementation
- Refactor pkg/idp
- Added tests to login

pkg/auth/idp/oauth2/config.go

@@ -19,10 +19,16 @@
 package oauth2
 
 import (
+	"strings"
+
 	"github.com/minio/console/pkg/auth/utils"
 	"github.com/minio/minio/pkg/env"
 )
 
+func GetSTSEndpoint() string {
+	return strings.TrimSpace(env.Get(ConsoleMinIOServer, "http://localhost:9000"))
+}
+
 func GetIdpURL() string {
 	return env.Get(ConsoleIdpURL, "")
 }
@@ -40,10 +46,6 @@ func GetIdpCallbackURL() string {
 	return env.Get(ConsoleIdpCallbackURL, "")
 }
 
-func GetIdpAdminRoles() string {
-	return env.Get(ConsoleIdpAdminRoles, "")
-}
-
 func IsIdpEnabled() bool {
 	return GetIdpURL() != "" &&
 		GetIdpClientID() != "" &&
@@ -64,8 +66,3 @@ var defaultSaltForIdpHmac = utils.RandomCharString(64)
 func getSaltForIdpHmac() string {
 	return env.Get(ConsoleIdpHmacSalt, defaultSaltForIdpHmac)
 }
-
-// GetSaltForIdpHmac returns the policy to be assigned to the users authenticating via an IDP
-func GetIDPPolicyForUser() string {
-	return env.Get(ConsoleIdpPolicyUser, "consoleAdmin")
-}