added security to the post of course and GET /courses

backend/src/main/java/ovh/herisson/Clyde/Services/CourseService.java

@@ -17,6 +17,8 @@ public class CourseService {
     }
 
     public Course save(Course course){
+        if (course.getOwner().getRole() != Role.Teacher)
+            return null;
         return courseRepo.save(course);
     }
 
@@ -24,6 +26,11 @@ public class CourseService {
         return courseRepo.findById(id);
     }
 
+
+    public Iterable<Course> findAll() {
+        return courseRepo.findAll();
+    }
+
     public boolean modifyData(long id, Map<String, Object> updates, Role role) {
         Course target = courseRepo.findById(id);
 
@@ -62,4 +69,5 @@ public class CourseService {
         courseRepo.save(target);
         return true;
     }
+
 }