1. A system, comprising: a first server managed by a content delivery network (CDN) service provider and comprising circuitry forming one or more processors coupled to memory holding non-transitory computer-program instructions to be executed by the one or more processors to cause the first server to: receive a first request from a client device over a network interface, the first request comprising an application programming interface (API) request; in response to the first request, determine a configuration file stored at the first server to apply for handling the request, the configuration file defining any of: recognized API endpoints and request forwarding instructions; identify, within the configuration file, a content control that indicates how to handle the first request from within a set of content controls stored at the first server in the configuration file; wherein the content control has a reference to an API endpoint content policy that controls, at least, request validation; extract an identifier from the first request, the extracted identifier comprising any of (i) at least part of a URI, (ii) at least part of a hostname, and (iii) at least part of a request header field; in response to the identification of the content control with the reference to the API endpoint content policy, send a second request that includes the extracted identifier to a remote host for the API endpoint content policy; receive the API endpoint content policy from the remote host in response to the second request, the API endpoint content policy comprising at least one of: (iv) an API resource model, and (v) an algorithm to compare the first request to an API resource model; wherein the API resource model comprises at least one of: (vi) designation of supported request methods, (vii) designation of valid URI path, (viii) designation of a valid URL query parameter resource, (ix) designation of arguments, parameters, or data necessary in requests; (x) designation of a parameter or limit specified for a user; apply the content control to the request at least by applying the API endpoint content policy to determine whether the first request conforms to the API resource model; after applying the content control and the API endpoint content policy, send at least a portion of the first request to a second server, the second server being an API origin for the API; the remote host comprising circuitry forming one or more processors coupled to memory holding non-transitory computer-program instructions to be executed by the one or more processors to cause the remote host to: receive the second request from the first server, with the extracted identifier; based at least in part on the extracted identifier, select the API endpoint content policy from amongst a plurality of API endpoint content policies stored at the remote host; send the API endpoint content policy to the first server, in response to the second request; wherein the first server is one of a plurality of distributed CDN servers, the first request is for a service accessible via the API, and the service enables any of: (i) interaction with a multi-tenant storage system operated by the CDN service provider on behalf of content providers, (ii) interaction with a multi-tenant computing system operated by the CDN service provider on behalf of content providers, and (iii) configuration by a CDN user of a CDN content delivery service, said configuration comprising configuration of CDN features and services for delivering any of a website and a web application on the CDN user's behalf over the CDN.