Google Cloud Endpoints + Firebase Auth: method_info is not set

So I am running the sample code provided by Google:

package com.neat.backend;
/**
 * An endpoint class we are exposing
 */
@Api(
        name = "myApi",
        version = "v1",
        namespace = @ApiNamespace(
                ownerDomain = "backend.neat.com",
                ownerName = "backend.neat.com",
                packagePath = ""
        ),
        issuers = {
        @ApiIssuer(
                name = "firebase",
                issuer = "https://securetoken.google.com/" + PROJECT_ID,
                jwksUri = "https://www.googleapis.com/robot/v1/metadata/x509/securetoken@system.gserviceaccount.com")
})
public class MyEndpoint {

    @ApiMethod(
            path = "firebase_user",
            httpMethod = ApiMethod.HttpMethod.GET,
            authenticators = {EspAuthenticator.class},
            issuerAudiences = {@ApiIssuerAudience(name = "firebase", audiences = {PROJECT_ID})}
    )
    public Email getUserEmailFirebase(User user) throws UnauthorizedException {
        if (user == null) {
            throw new UnauthorizedException("Invalid credentials");
        }

        Email response = new Email(user.getEmail());
        return response;
    }

}

I am getting a Firebase token from my Android client and try to send it to the backend by:

curl -H "Authorization: Bearer FIREBASE_JWT_TOKEN" \
     -X GET \
     http://localhost:8080/_ah/api/echo/v1/firebase_user

The error I see in the logs is the following:

[INFO] java.lang.IllegalStateException: method_info is not set in the request
[INFO]  at com.google.api.server.spi.auth.EspAuthenticator.authenticate(EspAuthenticator.java:67)
[INFO]  at com.google.api.server.spi.request.Auth.authenticate(Auth.java:100)
[INFO]  at com.google.api.server.spi.request.ServletRequestParamReader.getUser(ServletRequestParamReader.java:191)
[INFO]  at com.google.api.server.spi.request.ServletRequestParamReader.deserializeParams(ServletRequestParamReader.java:136)
[INFO]  at com.google.api.server.spi.request.RestServletRequestParamReader.read(RestServletRequestParamReader.java:123)
[INFO]  at com.google.api.server.spi.SystemService.invokeServiceMethod(SystemService.java:350)
[INFO]  at com.google.api.server.spi.handlers.EndpointsMethodHandler$RestHandler.handle(EndpointsMethodHandler.java:114)
[INFO]  at com.google.api.server.spi.handlers.EndpointsMethodHandler$RestHandler.handle(EndpointsMethodHandler.java:102)
[INFO]  at com.google.api.server.spi.dispatcher.PathDispatcher.dispatch(PathDispatcher.java:49)
[INFO]  at com.google.api.server.spi.EndpointsServlet.service(EndpointsServlet.java:71)
[INFO]  at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)

I have tried deploying the exact same code to App Engine and it works perfectly. I have tried debugging EspAuthenticator and it seems that it is expecting the Servlet filters to inject some attributes in the request.

It took me a while and a bit of debugging to realize that the filter that is supposed to inject method_info was not being fired.

I could fix it by modifying the mapping in web.xml adding the following dispatcher tags:

<filter-mapping>
    <filter-name>endpoints-api-configuration</filter-name>
    <servlet-name>EndpointsServlet</servlet-name>
    <dispatcher>REQUEST</dispatcher>
    <dispatcher>INCLUDE</dispatcher>
    <dispatcher>FORWARD</dispatcher>
</filter-mapping>