Resolve "Improve token usage for users"

Description

Related Issue

Motivation and Context

How Has This Been Tested?

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

Resolves to #378

controller/northbound/server/auth.go

@@ -95,7 +95,10 @@ func (s AuthServer) Login(ctx context.Context, request *apb.LoginRequest) (*apb.
 
 	userToUpdate.AddToken(token)
 	for len(userToUpdate.GetTokens()) > config.MaxTokensPerUser {
-		userToUpdate.RemoveToken(userToUpdate.GetTokens()[0])
+		err = userToUpdate.RemoveToken(userToUpdate.GetTokens()[0])
+		if err != nil {
+			return nil, err
+		}
 	}
 	err = s.userService.Update(userToUpdate)
 	if err != nil {