OAuth is an open standard that allows users to grant third-party websites and applications access to their information without sharing account credentials. This can be thought of as a form of access delegation because access to the user's account is being delegated to the third party. This is accomplished by prompting the user to confirm that they agree to permit the third party access to certain information about their account. Typically, this prop will specifically list which pieces of information or access are being requested. Once confirmed, the identity provider will supply the third party with a token that gives them access to the user's information. This token can then be used by the third party to access data or services offered by the identity provider directly on behalf of the user. OAuth is commonly used to grant access to third party applications, to APIs offered by large internet companies like Google, Microsoft, and Facebook. Let's say you want to use a third party meme creation website. This website lets you create memes using templates and gives you the option to save your creations and email them to your friends. Instead of the site sending the emails directly, which would appear to be coming from an address your friends wouldn't recognize, the site uses OAuth to get permission to send the memes using your email account directly. This is done by making an OAuth request to your email provider. Once you approve this request, the email provider issues an access token to the site, which grants the site access to your email account. The access token would have a scope, which says that it can only be used to access email, not other services associated with the account. So it can access email but not your cloud storage files or calendar, for example. It's important that users pay attention to what third party is requesting access and what exactly they're granting access to. OAuth permissions can be used in phishing style attacks to gain access to accounts without requiring credentials to be compromised. This works by sending phishing emails to potential victims that look like legitimate OAuth authorization requests, which ask the user to grant access to some aspects of their account through OAuth. Once the user grants access, the attacker has access to the account through the OAuth authorization token. This was used in an OAuth based worm attack in early 2017. There was a rash of phishing emails that appeared to be from a friend or colleague who wanted to share a google doc. When the sharing link was followed, the victim was prompted to log in and authorize access to email documents and contacts for some third party service, which only identified itself as the name Google Apps. But it was actually a malicious service that would then email contacts from their email account perpetuating the attack. In case you like to read more about it, I've included a link in the next reading. It's important to distinguish between OAuth and OpenID. OAuth is specifically an authorization system and OpenID is an authentication system. Though they're usually used together, OpenID Connect is an authentication layer built on top of OAuth 2.0 designed to improve upon OpenID and build better integration with OAuth authorizations. Since TACACS plus is a full AAA system, it also handles authorization along with authentication. This is done once a user is authenticated by allowing or disallowing access for the user account to run certain commands or access certain devices. This lets you not only allow admin access for users that administer devices while still allowing less privileged access to other users when necessary. Here's an example, since your networking teams are responsible for configuring and maintaining your network switches, routers, and other infrastructure. You'd give them admin access to your network and equipment. Meanwhile, you can have limited read-only access to your support team since they don't need to be able to make changes to switch configurations in their jobs. Read-only access is enough for them to troubleshoot problems. The rest of the user accounts would have no access at all and wouldn't be permitted to connect to the networking infrastructure. So more sophisticated or configurable AAA systems may even allow further refinement of authorization down to the command level. This gives you much more flexibility in how your access is granted to specific users or groups in your organization. RADIUS also allows you to authorize network access. For example, you may want to permit some users to have Wi-Fi and VPN access while others may not need this. When they authenticate to the RADIUS server, if the authentication succeeds, the RADIUS server returns configuration information to the network access server. This includes authorizations which specifies what network services the user is permitted to access.
