A computer-implemented method comprising: receiving, from a client device, a digital component request comprising a set of data; in response to receiving the digital component request: identifying one or more multi-stage workflows, each multi-stage workflow of the one or more multi-stage workflows (i) being configured to select digital components from candidate digital components of multiple content platforms and (ii) comprising one or more customizable stages; for each particular multi-stage workflow of the one or more multi-stage workflows: initiating, by a trusted execution environment, TEE, of a server, a sandbox environment for executing one or more stages of the particular multi-stage workflow; executing, by the TEE and within the sandbox environment, the one or more stages of the particular multi-stage workflow, wherein the sandbox environment prevents code of the multi-stage workflow from transmitting user data from the server; and receiving, by the server and from the TEE, output data from the particular multi-stage workflow; selecting, by the server, a digital component based on at least a portion of the output data from each particular multi-stage workflow; and providing, by the server, the digital component to the client device for presentation to the user of the client device. receiving, from a client device, a digital component request comprising a set of data; in response to receiving the digital component request: identifying one or more multi-stage workflows, each multi-stage workflow of the one or more multi-stage workflows (i) being configured to select digital components from candidate digital components of multiple content platforms and (ii) comprising one or more customizable stages; for each particular multi-stage workflow of the one or more multi-stage workflows: initiating, by a trusted execution environment, TEE, of a server, a sandbox environment for executing one or more stages of the particular multi-stage workflow; executing, by the TEE and within the sandbox environment, the one or more stages of the particular multi-stage workflow, wherein the sandbox environment prevents code of the multi-stage workflow from transmitting user data from the server; and receiving, by the server and from the TEE, output data from the particular multi-stage workflow; selecting, by the server, a digital component based on at least a portion of the output data from each particular multi-stage workflow; and providing, by the server, the digital component to the client device for presentation to the user of the client device. identifying one or more multi-stage workflows, each multi-stage workflow of the one or more multi-stage workflows (i) being configured to select digital components from candidate digital components of multiple content platforms and (ii) comprising one or more customizable stages; for each particular multi-stage workflow of the one or more multi-stage workflows: initiating, by a trusted execution environment, TEE, of a server, a sandbox environment for executing one or more stages of the particular multi-stage workflow; executing, by the TEE and within the sandbox environment, the one or more stages of the particular multi-stage workflow, wherein the sandbox environment prevents code of the multi-stage workflow from transmitting user data from the server; and receiving, by the server and from the TEE, output data from the particular multi-stage workflow; initiating, by a trusted execution environment, TEE, of a server, a sandbox environment for executing one or more stages of the particular multi-stage workflow; executing, by the TEE and within the sandbox environment, the one or more stages of the particular multi-stage workflow, wherein the sandbox environment prevents code of the multi-stage workflow from transmitting user data from the server; and receiving, by the server and from the TEE, output data from the particular multi-stage workflow; selecting, by the server, a digital component based on at least a portion of the output data from each particular multi-stage workflow; and providing, by the server, the digital component to the client device for presentation to the user of the client device.