gRPC supports a number of different mechanisms for asserting identity between an client and server. This document provides code samples demonstrating how to provide SSL/TLS encryption support and identity assertions in Java, as well as passing OAuth2 tokens to services that support it.

HTTP/2 over TLS mandates the use of ALPN to negotiate the use of the h2 protocol. ALPN is a fairly new standard and (where possible) gRPC also supports protocol negotiation via NPN for systems that do not yet support ALPN.

On Android, use the Play Services Provider. For non-Android systems, use OpenSSL.

On Android we recommend the use of the Play Services Dynamic Security Provider to ensure your application has an up-to-date OpenSSL library with the necessary ciper-suites and a reliable ALPN implementation.

You may need to update the security provider to enable ALPN support, especially for Android versions < 5.0. If the provider fails to update, ALPN may not work.

This is currently the recommended approach for using gRPC over TLS (on non-Android systems).

The main benefits of using OpenSSL are:

1. Speed: In local testing, we've seen performance improvements of 3x over the JDK. GCM, which is used by the only cipher suite required by the HTTP/2 spec, is 10-500x faster.
2. Ciphers: OpenSSL has its own ciphers and is not dependent on the limitations of the JDK. This allows supporting GCM on Java 7.
3. ALPN to NPN Fallback: if the remote endpoint doesn't support ALPN.
4. Version Independence: does not require using a different library version depending on the JDK update.

Support for OpenSSL is only provided for the Netty transport via netty-tcnative, which is a fork of Apache Tomcat's tcnative, a JNI wrapper around OpenSSL.

As of version 1.1.33.Fork14, netty-tcnative provides two options for usage: statically or dynamically linked. For simplification of initial setup, we recommend that users first look at netty-tcnative-boringssl-static, which is statically linked against BoringSSL and Apache APR. Using this artifact requires no extra installation and guarantees that ALPN and the ciphers required for HTTP/2 are available. In addition, starting with 1.1.33.Fork16 binaries for all supported platforms can be included at compile time and the correct binary for the platform can be selected at runtime.

Production systems, however, may require an easy upgrade path for OpenSSL security patches. In this case, relying on the statically linked artifact also implies waiting for the Netty team to release the new artifact to Maven Central, which can take some time. A better solution in this case is to use the dynamically linked netty-tcnative artifact, which allows the site administrator to easily upgrade OpenSSL in the standard way (e.g. apt-get) without relying on any new builds from Netty.

This is the simplest way to configure the Netty transport for OpenSSL. You just need to add the appropriate netty-tcnative-boringssl-static artifact to your application's classpath.

Artifacts are available on Maven Central for the following platforms:

In Maven, you can use the os-maven-plugin to help simplify the dependency.

<project>
  <dependencies>
    <dependency>
      <groupId>io.netty</groupId>
      <artifactId>netty-tcnative-boringssl-static</artifactId>
      <version>1.1.33.Fork25</version>
    </dependency>
  </dependencies>
</project>

Gradle you can use the osdetector-gradle-plugin, which is a wrapper around the os-maven-plugin.

buildscript {
  repositories {
    mavenCentral()
  }
}

dependencies {
    compile 'io.netty:netty-tcnative-boringssl-static:1.1.33.Fork25'
}

If for any reason you need to dynamically link against OpenSSL (e.g. you need control over the version of OpenSSL), you can instead use the netty-tcnative artifact.

Requirements:

1. OpenSSL version >= 1.0.2 for ALPN support, or version >= 1.0.1 for NPN.
2. Apache APR library (libapr-1) version >= 1.5.2.
3. netty-tcnative version >= 1.1.33.Fork7 must be on classpath. Prior versions only supported NPN and only Fedora-derivatives were supported for Linux.

Artifacts are available on Maven Central for the following platforms:

On Linux it should be noted that OpenSSL uses a different soname for Fedora derivatives than other Linux releases. To work around this limitation, netty-tcnative deploys two separate versions for linux.

In Maven, you can use the os-maven-plugin to help simplify the dependency.

<project>
  <dependencies>
    <dependency>
      <groupId>io.netty</groupId>
      <artifactId>netty-tcnative</artifactId>
      <version>1.1.33.Fork25</version>
      <classifier>${tcnative.classifier}</classifier>
    </dependency>
  </dependencies>

  <build>
    <extensions>
      <!-- Use os-maven-plugin to initialize the "os.detected" properties -->
      <extension>
        <groupId>kr.motd.maven</groupId>
        <artifactId>os-maven-plugin</artifactId>
        <version>1.4.0.Final</version>
      </extension>
    </extensions>
    <plugins>
      <!-- Use Ant to configure the appropriate "tcnative.classifier" property -->
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-antrun-plugin</artifactId>
        <executions>
          <execution>
            <phase>initialize</phase>
            <configuration>
              <exportAntProperties>true</exportAntProperties>
              <target>
                <condition property="tcnative.classifier"
                           value="${os.detected.classifier}-fedora"
                           else="${os.detected.classifier}">
                  <isset property="os.detected.release.fedora"/>
                </condition>
              </target>
            </configuration>
            <goals>
              <goal>run</goal>
            </goals>
          </execution>
        </executions>
      </plugin>
    </plugins>
  </build>
</project>

Gradle you can use the osdetector-gradle-plugin, which is a wrapper around the os-maven-plugin.

buildscript {
  repositories {
    mavenCentral()
  }
  dependencies {
    classpath 'com.google.gradle:osdetector-gradle-plugin:1.4.0'
  }
}

// Use the osdetector-gradle-plugin
apply plugin: "com.google.osdetector"

def tcnative_classifier = osdetector.classifier;
// Fedora variants use a different soname for OpenSSL than other linux distributions
// (see http://netty.io/wiki/forked-tomcat-native.html).
if (osdetector.os == "linux" && osdetector.release.isLike("fedora")) {
  tcnative_classifier += "-fedora";
}

dependencies {
    compile 'io.netty:netty-tcnative:1.1.33.Fork25:' + tcnative_classifier
}

WARNING: DON'T DO THIS!!

For non-Android systems, the recommended approach is to use OpenSSL. Using the JDK for ALPN is generally much slower and may not support the necessary ciphers for HTTP2.

Jetty ALPN brings its own baggage in that the Java bootclasspath needs to be modified, which may not be an option for some environments. In addition, a specific version of Jetty ALPN has to be used for a given version of the JRE. If the versions don't match the negotiation will fail, but you won't really know why. And since there is such a tight coupling between Jetty ALPN and the JRE, there are no guarantees that Jetty ALPN will support every JRE out in the wild.

The moral of the story is: Don't use the JDK for ALPN! But if you absolutely have to, here's how you do it... :)

If not using the Netty transport (or you are unable to use OpenSSL for some reason) another alternative is to use the JDK for TLS.

No standard Java release has built-in support for ALPN today (there is a tracking issue so go upvote it!) so we need to use the Jetty-ALPN (or Jetty-NPN if on Java < 8) bootclasspath extension for OpenJDK. To do this, add an Xbootclasspath JVM option referencing the path to the Jetty alpn-boot jar.

java -Xbootclasspath/p:/path/to/jetty/alpn/extension.jar ...

Note that you must use the release of the Jetty-ALPN jar specific to the version of Java you are using. However, you can use the JVM agent Jeety-ALPN-Agent to load the correct Jetty alpn-boot jar file for the current Java version. To do this, instead of adding an Xbootclasspath option, add a javaagent JVM option referencing the path to the Jetty alpn-agent jar.

java -javaagent:/path/to/jetty-alpn-agent.jar ...

Java 7 does not support the cipher suites recommended by the HTTP2 specification. To address this we suggest servers use Java 8 where possible or use an alternative JCE implementation such as Bouncy Castle. If this is not practical it is possible to use other ciphers but you need to ensure that the services you intend to call have allowed out-of-spec ciphers and have evaluated the security risks of doing so.

Users should be aware that GCM is very slow (1 MB/s) before Java 8u60. With Java 8u60 GCM is 10x faster (10-20 MB/s), but that is still slow compared to OpenSSL (~200 MB/s), especially with AES-NI support (~1 GB/s). GCM cipher suites are the only suites available that comply with HTTP2's cipher requirements.

Some web containers, such as Jetty restrict access to server classes for web applications. A gRPC client running within such a container must be properly configured to allow access to the ALPN classes. In Jetty, this is done by including a WEB-INF/jetty-env.xml file containing the following:

<?xml version="1.0"  encoding="ISO-8859-1"?>
<!DOCTYPE Configure PUBLIC "-//Mort Bay Consulting//DTD Configure//EN" "http://www.eclipse.org/jetty/configure.dtd">
<Configure class="org.eclipse.jetty.webapp.WebAppContext">
    <!-- Must be done in jetty-env.xml, since jetty-web.xml is loaded too late.   -->
    <!-- Removing ALPN from the blacklisted server classes (using "-" to remove). -->
    <!-- Must prepend to the blacklist since order matters.                       -->
    <Call name="prependServerClass">
        <Arg>-org.eclipse.jetty.alpn.</Arg>
    </Call>
</Configure>

To use TLS on the server, a certificate chain and private key need to be specified in PEM format. The standard TLS port is 443, but we use 8443 below to avoid needing extra permissions from the OS.

Server server = ServerBuilder.forPort(8443)
    // Enable TLS
    .useTransportSecurity(certChainFile, privateKeyFile)
    .addService(serviceImplementation)
    .build();
server.start();

If the issuing certificate authority is not known to the client then a properly configured SslContext or SSLSocketFactory should be provided to the NettyChannelBuilder or OkHttpChannelBuilder, respectively.

Mutual authentication (or "client-side authentication") configuration is similar to the server by providing truststores, a client certificate and private key to the client channel. The server must also be configured to request a certificate from clients, as well as truststores for which client certificates it should allow.

Server server = NettyServerBuilder.forPort(8443)
    .sslContext(GrpcSslContexts.forServer(certChainFile, privateKeyFile)
        .trustManager(clientCertChainFile)
        .clientAuth(ClientAuth.OPTIONAL)
        .build());

Negotiated client certificates are available in the SSLSession, which is found in the SSL_SESSION_KEY attribute of ServerCall. A server interceptor can provide details in the current Context.

public final static Context.Key<SSLSession> SSL_SESSION_CONTEXT = Context.key("SSLSession");

@Override
public <ReqT, RespT> ServerCall.Listener<ReqT> interceptCall(ServerCall<RespT> call, 
    Metadata headers, ServerCallHandler<ReqT, RespT> next) {
    SSLSession sslSession = call.attributes().get(ServerCall.SSL_SESSION_KEY);
    if (sslSession == null) {
        return next.startCall(call, headers)
    }
    return Contexts.interceptCall(
        Context.current().withValue(SSL_SESSION_CONTEXT, clientContext), call, headers, next);
}

An option is provided to use gRPC over plaintext without TLS. While this is convenient for testing environments, users must be aware of the security risks of doing so for real production systems.

The following code snippet shows how you can call the Google Cloud PubSub API using gRPC with a service account. The credentials are loaded from a key stored in a well-known location or by detecting that the application is running in an environment that can provide one automatically, e.g. Google Compute Engine. While this example is specific to Google and it's services, similar patterns can be followed for other service providers.

// Create a channel to the test service.
ManagedChannel channel = ManagedChannelBuilder.forTarget("pubsub.googleapis.com")
    .build();
// Get the default credentials from the environment
GoogleCredentials creds = GoogleCredentials.getApplicationDefault();
// Down-scope the credential to just the scopes required by the service
creds = creds.createScoped(Arrays.asList("https://www.googleapis.com/auth/pubsub"));
// Create an instance of {@link io.grpc.CallCredentials}
CallCredentials callCreds = MoreCallCredentials.from(creds);
// Create a stub with credential
PublisherGrpc.PublisherBlockingStub publisherStub =
    PublisherGrpc.newBlockingStub(channel).withCallCredentials(callCreds);
publisherStub.publish(someMessage);