Add method to get access token by providing refresh token in case of offline_access scope

src/main/java/eu/dnetlib/authentication/entities/TokenResponse.java

@@ -0,0 +1,2 @@
+package eu.dnetlib.authentication.entities;public class TokenResponse {
+}

src/main/java/eu/dnetlib/authentication/services/SecurityService.java

@@ -0,0 +1,2 @@
+package eu.dnetlib.authentication.services;public class SecurityService {
+}