API

What Appian APIs are for is to expose Appian processes as services that other systems (such as websites) can utilize.  For instance, if you want your website to look up some financial data and run through a bunch of business rules and spit out the results, you can make that stuff in Appian and expose through the API.  Website gets the JSON Appian makes, and you do with your JSON what you want.

This is nothing at all like logging users in. 

You can create an ersatz login using Appian Portals, but that's to allow users to use the limited Portals functionality in a sort-of-logged-in way, while keeping them siloed away from the real Appian and real functionality.  See if Portals provides the functionality you need.  Also, you could look at embedded interfaces.

Or, maybe what you really want to make is just an Appian installation with Appian apps and Sites pages.  One use for Portals is to have anonymous users request login credentials for Appian.  When they get login credentials, it's just Appian after that.

What Appian APIs are for is to expose Appian processes as services that other systems (such as websites) can utilize.  For instance, if you want your website to look up some financial data and run through a bunch of business rules and spit out the results, you can make that stuff in Appian and expose through the API.  Website gets the JSON Appian makes, and you do with your JSON what you want.

This is nothing at all like logging users in. 

You can create an ersatz login using Appian Portals, but that's to allow users to use the limited Portals functionality in a sort-of-logged-in way, while keeping them siloed away from the real Appian and real functionality.  See if Portals provides the functionality you need.  Also, you could look at embedded interfaces.

Or, maybe what you really want to make is just an Appian installation with Appian apps and Sites pages.  One use for Portals is to have anonymous users request login credentials for Appian.  When they get login credentials, it's just Appian after that.