Error 400 when using box-java-sdk

We copied and pasted the Box SDK sample code for authenticating:

https://github.com/box/box-java-sdk/blob/master/src/example/java/com/box/sdk/example/AccessAsAppUser.java

We generated a key pair using instructions from: https://docs.box.com/docs/app-auth#section-1-generating-an-rsa-keypair:

openssl genrsa -aes256 -out private_key.pem 2048
openssl rsa -pubout -in private_key.pem -out public_key.pem

We pasted in the public key in the app settings, and use the configuration other settings (client id, etc.) and  get a 400 response error.

Code:

import com.box.sdk.*;

private String CLIENT_ID = "****";
private String CLIENT_SECRET = "****";
private String USER_ID = "****";
private String PUBLIC_KEY_ID = "****";
private String PRIVATE_KEY_FILE = "****";
private String PRIVATE_KEY_PASSWORD = "****";
private int MAX_DEPTH = 1;
private int MAX_CACHE_ENTRIES = 100;

public void testAppUser () {

   try {
        String privateKey = new String(Files.readAllBytes(Paths.get(PRIVATE_KEY_FILE)));
        JWTEncryptionPreferences encryptionPref = new JWTEncryptionPreferences();
        encryptionPref.setPublicKeyID(PUBLIC_KEY_ID);
        encryptionPref.setPrivateKey(privateKey); //
        encryptionPref.setPrivateKeyPassword(PRIVATE_KEY_PASSWORD);
        encryptionPref.setEncryptionAlgorithm(EncryptionAlgorithm.RSA_SHA_256);
     
        IAccessTokenCache accessTokenCache = new InMemoryLRUAccessTokenCache(MAX_CACHE_ENTRIES);

        BoxDeveloperEditionAPIConnection api = BoxDeveloperEditionAPIConnection.getAppUserConnection(USER_ID, CLIENT_ID,
            CLIENT_SECRET, encryptionPref, accessTokenCache);

        BoxUser.Info userInfo = BoxUser.getCurrentUser(api).getInfo();
        System.out.format("Welcome, %s!\n\n", userInfo.getName());

        } catch (IOException e) {
            new RuntimeException("Error message", e).printStackTrace();
        }
}

Response:

Whitelabel Error Page
This application has no explicit mapping for /error, so you are seeing this as a fallback.
Fri Apr 07 15:19:40 PDT 2017
There was an unexpected error (type=Internal Server Error, status=500).
The API returned an error code: 400

com.box.sdk.BoxAPIException: The API returned an error code: 400
        at com.box.sdk.BoxAPIResponse.(BoxAPIResponse.java:69) ~[box-java-sdk-2.3.0.jar!/:na]
        at com.box.sdk.BoxJSONResponse.(BoxJSONResponse.java:30) ~[box-java-sdk-2.3.0.jar!/:na]
        at com.box.sdk.BoxAPIRequest.trySend(BoxAPIRequest.java:423) ~[box-java-sdk-2.3.0.jar!/:na]
        at com.box.sdk.BoxAPIRequest.send(BoxAPIRequest.java:209) ~[box-java-sdk-2.3.0.jar!/:na]
        at com.box.sdk.BoxAPIRequest.send(BoxAPIRequest.java:184) ~[box-java-sdk-2.3.0.jar!/:na]
        at com.box.sdk.BoxDeveloperEditionAPIConnection.authenticate(BoxDeveloperEditionAPIConnection.java:245) ~[box-java-sdk-2.3.0.jar!/:na]
        at com.box.sdk.BoxDeveloperEditionAPIConnection.tryRestoreUsingAccessTokenCache(BoxDeveloperEditionAPIConnection.java:305) ~[box-java-sdk-2.3.0.jar!/:na]
        at com.box.sdk.BoxDeveloperEditionAPIConnection.getAppUserConnection(BoxDeveloperEditionAPIConnection.java:212) ~[box-java-sdk-2.3.0.jar!/:na]
        at service.Box.testAppUser(Box.java:56) ~[classes!/:0.0.1-SNAPSHOT]
        at service.BoxuploadController.testAppUser(BoxuploadController.java:42) ~[classes!/:0.0.1-SNAPSHOT]
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_121]
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_121]
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_121]
        at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_121]
        at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:205) ~[spring-web-4.3.6.RELEASE.jar!/:4.3.6.RELEASE]
        at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:133) ~[spring-web-4.3.6.RELEASE.jar!/:4.3.6.RELEASE]
        at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:116) ~[spring-webmvc-4.3.6.RELEASE.jar!/:4.3.6.RELEASE]
        at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:827) ~[spring-webmvc-4.3.6.RELEASE.jar!/:4.3.6.RELEASE]
        at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:738) ~[spring-webmvc-4.3.6.RELEASE.jar!/:4.3.6.RELEASE]
        at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:85) ~[spring-webmvc-4.3.6.RELEASE.jar!/:4.3.6.RELEASE]
        at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:963) ~[spring-webmvc-4.3.6.RELEASE.jar!/:4.3.6.RELEASE]
        at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:897) ~[spring-webmvc-4.3.6.RELEASE.jar!/:4.3.6.RELEASE]
        at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:970) ~[spring-webmvc-4.3.6.RELEASE.jar!/:4.3.6.RELEASE]
        at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:861) ~[spring-webmvc-4.3.6.RELEASE.jar!/:4.3.6.RELEASE]
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:622) ~[tomcat-embed-core-8.5.11.jar!/:8.5.11]
        at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:846) ~[spring-webmvc-4.3.6.RELEASE.jar!/:4.3.6.RELEASE]
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:729) ~[tomcat-embed-core-8.5.11.jar!/:8.5.11]
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:230) ~[tomcat-embed-core-8.5.11.jar!/:8.5.11]
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165) ~[tomcat-embed-core-8.5.11.jar!/:8.5.11]
        at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52) ~[tomcat-embed-websocket-8.5.11.jar!/:8.5.11]
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:192) ~[tomcat-embed-core-8.5.11.jar!/:8.5.11]
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165) ~[tomcat-embed-core-8.5.11.jar!/:8.5.11]
        at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:99) ~[spring-web-4.3.6.RELEASE.jar!/:4.3.6.RELEASE]
        at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring-web-4.3.6.RELEASE.jar!/:4.3.6.RELEASE]
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:192) ~[tomcat-embed-core-8.5.11.jar!/:8.5.11]
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165) ~[tomcat-embed-core-8.5.11.jar!/:8.5.11]
        at org.springframework.web.filter.HttpPutFormContentFilter.doFilterInternal(HttpPutFormContentFilter.java:105) ~[spring-web-4.3.6.RELEASE.jar!/:4.3.6.RELEASE]
        at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring-web-4.3.6.RELEASE.jar!/:4.3.6.RELEASE]
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:192) ~[tomcat-embed-core-8.5.11.jar!/:8.5.11]
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165) ~[tomcat-embed-core-8.5.11.jar!/:8.5.11]
        at org.springframework.web.filter.HiddenHttpMethodFilter.doFilterInternal(HiddenHttpMethodFilter.java:81) ~[spring-web-4.3.6.RELEASE.jar!/:4.3.6.RELEASE]
        at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring-web-4.3.6.RELEASE.jar!/:4.3.6.RELEASE]
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:192) ~[tomcat-embed-core-8.5.11.jar!/:8.5.11]
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165) ~[tomcat-embed-core-8.5.11.jar!/:8.5.11]
        at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:197) ~[spring-web-4.3.6.RELEASE.jar!/:4.3.6.RELEASE]
        at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring-web-4.3.6.RELEASE.jar!/:4.3.6.RELEASE]
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:192) ~[tomcat-embed-core-8.5.11.jar!/:8.5.11]
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165) ~[tomcat-embed-core-8.5.11.jar!/:8.5.11]
        at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:198) ~[tomcat-embed-core-8.5.11.jar!/:8.5.11]
        at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96) [tomcat-embed-core-8.5.11.jar!/:8.5.11]
        at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:474) [tomcat-embed-core-8.5.11.jar!/:8.5.11]
        at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:140) [tomcat-embed-core-8.5.11.jar!/:8.5.11]
        at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79) [tomcat-embed-core-8.5.11.jar!/:8.5.11]
        at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:87) [tomcat-embed-core-8.5.11.jar!/:8.5.11]
        at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:349) [tomcat-embed-core-8.5.11.jar!/:8.5.11]
        at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:783) [tomcat-embed-core-8.5.11.jar!/:8.5.11]
        at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66) [tomcat-embed-core-8.5.11.jar!/:8.5.11]
        at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:798) [tomcat-embed-core-8.5.11.jar!/:8.5.11]
        at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1434) [tomcat-embed-core-8.5.11.jar!/:8.5.11]
        at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) [tomcat-embed-core-8.5.11.jar!/:8.5.11]
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) [na:1.8.0_121]
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) [na:1.8.0_121]
        at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) [tomcat-embed-core-8.5.11.jar!/:8.5.11]
        at java.lang.Thread.run(Thread.java:745) [na:1.8.0_121]

- Any ideas on what to look at, or how to resolve this?