<?php header("Access-Control-Allow-Origin: *");

Pra usar basta usar a url:
-- https://proxier.now.sh/api?url=https://viacep.com.br/ws/<SEU_CEP_AQUI>/json

//Access to XMLHttpRequest at 'http://localhost/[api path].php' from origin 'http://localhost:4200' has been blocked by CORS policy: Request header field content-type is not allowed by Access-Control-Allow-Headers in preflight response.
//The error is simply saying that "Content-Type" is missing from "Access-Control-Allow-Headers".
//Therefore we need to add "Content-Type" to "Access-Control-Allow-Headers".
<?php
header('Access-Control-Allow-Headers: Content-Type');
-----
?>

@Configuration
@EnableWebMvc
public class WebConfig extends WebMvcConfigurerAdapter { @Override public void addCorsMappings(CorsRegistry registry) { registry.addMapping("/api/**") .allowedOrigins("http://domain2.com") .allowedMethods("PUT", "DELETE") .allowedHeaders("header1", "header2", "header3") .exposedHeaders("header1", "header2") .allowCredentials(false).maxAge(3600); }
}

@CrossOrigin(origins = "http://localhost:4200")
@RestController
@RequestMapping("/api/v1/")
public class EmployeeController {
// ..
}

@Configuration
@EnableWebMvc
public class WebConfig extends WebMvcConfigurerAdapter { @Override public void addCorsMappings(CorsRegistry registry) { registry.addMapping("/**"); }
}