Detecting accounts owned by a user and displaying last signed in.

We were talking about networking devices in the earlier post. While shared devices seem to be shrinking in number and personal devices seem to be growing in number, we face all the more question on whether those devices are secured. Identity is used to login to a device or site and usually consists of a username and a credential. With the devices becoming personal, a user may remain signed in to the device since it is physically secured by her. 

An owner may want to sign in with different credentials if she wants to separate the concerns by authenticating and performing actions under a different login. This may not be typical in every day use but having more than one account to your blog or email provider or another company website is altogether very common.

When an owner wants more than one identities created, usually she gives them a different name. While many take the precaution of using a common prefix or suffix to recognizes these different accounts, they are not necessarily required. Consequently, grouping the different accounts for the same person is not easy except by the owner when she recalls all that she created.  On the other hand, when the account is created and if we can leave an annotation or allow the account creation process to read the previously used account from the devices, some associations may be set up. This is very helpful to group the accounts. The step does not need to be taken only at registration time but can be taken at any time after that should the owner want to tag different accounts. Otherwise we are left to discovering these related accounts by matches in first name, last name and some other fields such as recovery email.

Discovering related accounts is one thing. Presenting those to the user for actions such as deletion is another thing. Just like we display last signed in activity for different devices as a security measure for the user, we can could also display related accounts for account hygiene by the owner.

For businesses, the use case for displaying the last-signed-in-on-device activity is perhaps more relevant than showing related accounts but this may change quickly with the ability to switch accounts when shown on the login page.

#codingexercise
we were discussing bridges and torches problem and how the participants can either be on the left or right side of bridge.
if we use a bitmask for their presence on one side of bridge, we can quickly calculate the other side as follows: 
To get the right mask value we can use:
int GetLeftMask(int rightmask)
{
// use the 1s in all positions of the number and xor it with the right mask
return ((1 << n) - 1) ^ rightmask;
}