Avenger Penguin

Authorisation vs. Authentication and why we should care

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At some point whilst interacting with many websites or web-based applications and services, users are asked to state and prove who they are. Whether this is to make sure only that user edits their own profile or it is for secure financial transactions, identity, trust and authorisation underpin almost any secure communication. Here, I will break down the basic, distinct components of user identification and show why the distinction between them is important for designing or even using a secure system.

Defining the Difference

The first division — and the one discussed in this post — is the difference between the process of authentication and that of authorisation. Given that many people use one term to cover both processes, the distinction might seem pedantic, but understanding the divide can greatly improve the user-friendliness and security of an application. Authentication can be said to be broken down into trust and identity, but that will be discussed in another post.

In short, authentication is the act of getting a person to say who they are and then to confirm they are indeed that person. In contrast, authorisation already assumes that individual is who they say they are, but goes further to confirm they are permitted to see the resource or perform the action they are requesting. In essence, this breaks down a login process into two questions:

  1. Who is this person?
  2. What may this person see or do?

A suitable analogy here can be made with credit card purchases in a shop. Signing a receipt — assuming it matches that on the back of your card — or entering your PIN into a Chip and PIN device is the authentication process. The assumption is that only the true card owner would normally be able to replicate the signature or know the corresponding PIN, but this still does not guarantee the transaction will continue through to completion.

This is because the next and final step is for the bank to be contacted to decide whether you actually have enough funds or credit remaining to make the purchase. Here, the bank is happy that the user’s identity has already been confirmed by signature or PIN and it is only concerned with authorising the desired request for funds.

Authentication and Authorisation in Web Applications

When designing the flow of an application, the best user experience comes from only authenticating once, but authorising on every request after that. A large number of applications achieve this by asking the user to login before the first privileged request and then storing their login into a session or cookie. No sensible website asks a user to log in again every time they do anything.

Note the distinction coming into play in that all future requests will assume that cookie or session is truthful when it asserts which user is currently logged in. This highlights a very important part of security where it should not be possible for a malicious person to forge the necessary information to claim they are already logged in as user.

For developers, this means storing a random session ID in the cookie after login as opposed to storing the user ID, which can be forged easily.

What about the experience for the user? There is a good reason why the HTTP response codes have the distinction of “401 Unauthorized” and “403 Forbidden”. Annoyingly, even the HTTP specification itself here is using the terms authorisation and authentication interchangeably. More accurate would be to call the former “401 Not authenticated” and the latter “403 Not authorised”.

The reason for this is that the 401 response is telling the user or web browser that this particular resource cannot be accessed by just anyone and you are expected to come back with proof of identity. The most common outcome here is that the web browser will display a box asking for a username and password and will then send those over automatically without the user necessarily knowing the exact process behind the scenes.

Once the user is logged in, the website is still normally going to do the authorisation process to check that the authenticated user is permitted to see or do this exact resource or action, e.g. I may be logged into Facebook as a valid user, but I should not be permitted to edit another user’s profile. If the user is permitted, they get the page they wanted successfully — normally HTTP status code 200 “OK” — but if they are still not allowed to be here, they get the “403 Forbidden” response.

Corporate and University Networks

This duality of authentication and authorisation plays out very strongly in a large environment such as a corporation or a university. Most enterprise-level computer networks in these institutions will have a central user directory that can be consulted whenever anybody wants to log in to a computer, a web application or any other system that needs to be secured.

Whilst every system will contact the same user directory, it is very unlikely that all users will have access to everything. Senior managers may have sole access to the most confidential company data or a university may have internal systems only accessible by staff and not students. Some resources may be restricted to certain departments only.

To this end, all systems and applications are going to perform a two-step process — just as with credit card purchases — before allowing a user access. The first will be to authenticate their username and password and the second will be to check extra information about the user to confirm they are authorised to have access. Generally, user directories will have extra attributes about each user such as department and allow the administrators to put people into other custom groups that reflect however people may be grouped together in the organisation. For example, a user may have to be in the “Payroll” group to access the payroll system.

Most applications will internalise this two-step procedure so it appears to the user as only one step from entering login details and gaining access to the system. In light of this, why discuss the authentication/authorisation distinction at all here? The reasons are two-fold.

The first consideration is user-friendliness of the login process. If the only two outcomes of a login attempt are success (access is granted) or failure (access is not granted), the user is none the wiser as to whether they entered their password incorrectly or whether they are not sufficiently privileged enough to be allowed into this system. A less frustrating set of outcomes would be success, Not Authenticated and Not Authorised.

Here, the application is explaining which of the two steps went wrong for the user. If the authentication stage failed, then the user can be returned back to the login page with a message saying their login details were not recognised (so the user can try their password again or contact IT support to see if their account was suspended/removed for any reason). If the problem lay in the authorisation step, then the user can be informed there was nothing wrong with their password and present a more helpful message including details of how to gain access to this system if they believe they should have it. This is normally a more administrative task of adjusting their user account to be in the correct group rather than a technical fault.

The second issue concerns user-friendliness as well, but is more about fighting a problem that arises in any large organisation that has several computer systems. For example, an employee of a payroll department may come into to work each morning, log in to their PC and throughout the day have to log in again to:

Whilst having a central user directory for all these systems to consult for verifying usernames and passwords means this employee only has to remember one password (and if they change it, it changes for all systems in one go), it does not save them from having to type it in several times in one day. This is because it is common for corporate systems to have their own individual login pages that link up to your user directory, but still each perform both steps of authentication and authorisation individually as well.

Single Sign-on

Anything designed as a solution to the aforementioned problem is known as Single sign-on or SSO as it is commonly called. An SSO setup within an organisation will ensure the user only types their username and password in once — per day, usually — and that action is then propagated to all systems who then trust the fact that the user has already identified themselves.

More abstractly, this is a setup where all the applications no longer do the authentication step and instead go straight to the authorisation step. The authentication process has been moved out to a single login page/screen and there exists some mechanism by which the login process passes over to these applications the name of the person that has been logged in.

It can be thought of as a building with a single security desk at the front. People entering the building are asked to show ID and are then issued with a security card valid for that day which allows them to access areas of the building they are permitted to enter as freely as they like. This card contrasts the cumbersome approach of having an ID checkpoint at every door in the building.

The drawback with this setup is that many commercial applications are not designed to integrate nicely with many SSO systems, but it is certainly simple to build support into any applications developed within the organisation. Many people who have experienced higher education will have already used an SSO setup if they have used any of the following:

With Athens or Shibboleth, students are asked to log in whenever they wish to access an external, educational resource for which their university is paying a licence, but — so long as they do not close their browser — are not asked to do so again even if they proceed to view other resources they are also permitted to access. It is entirely possible to merge this with an internal SSO system so that the moment a user logs into anything once, they have an unhindered pass to browse all permitted resources, internal or external.

A comparison of technical solutions for SSO will be discussed in a future post.


Despite the important distinction between the two processes of authentication and authorisation, they do remain a tightly-coupled pair in a security system. Authorisation is meaningless without a proper authentication procedure that can be trusted to verify people’s identity accurately. For example, imagine a credit card transaction that authorised funds for a purchase without the buyer having signed anything nor entered their PIN.

Further Considerations

In this post, the authentication process was assumed mostly to be the recognisable username and password combination. What has not been discussed is:

These will be addressed in a future post. Also, there will be another article to show how the same theory behind authentication is important for the reverse process of a user verifying a website is who it claims to be, e.g. that you are looking at your bank’s legitimate website and not an imitation set up to steal your account details.