The IXMP REST API, or Application Programming Interface, is an interface that allows programatically using the ix modeling platform (ixmp), a data warehouse for scenario analysis.
IXMP and its REST API are the backbone of IIASA's Scenario Explorer, but they can also be used and accessed by a wide range of programming languages, applications or scripts. This allows, for example, building web-based tools that visualize or otherwise use data included in a Scenario Explorer instance such as the IAMC 1.5C Scenario Explorer.
The credentials and permissions of an IXMP REST API are managed by a separate ENE Authentication Server. Thus, the login part - getting an access token and getting/setting user permissions - is handled via the authentication server. The actual modeling/scenario data are then accessed via the IXMP REST API, using the token and permissions received by the authentication server.
The full documentation of the IXMP REST API, which includes information about accessing the separate Authentication server, is available at:

The IXMP REST API was initially developed at IIASA under the SENSES project which is part of the JPI Climate ERA-Net Cofund for Climate Services with co-funding by the European Union under grant agreement No. 690462, the Austrian Federal Ministry of Science and Research via the Austrian Research Promotion Agency (FFG).