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 and support for the GCM mode of AES.

There are multiple options available, but on Android we recommend using the Play Services Provider and for non-Android systems we recommend netty-tcnative with BoringSSL.

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 cipher-suites and a reliable ALPN implementation. This requires updating the security provider at runtime.

Although ALPN mostly works on newer Android releases (especially since 5.0), there are bugs and discovered security vulnerabilities that are only fixed by upgrading the security provider. Thus, we recommend using the Play Service Dynamic Security Provider for all Android versions.

Note: The Dynamic Security Provider must be installed before creating a gRPC OkHttp channel. gRPC's OkHttpProtocolNegotiator statically initializes the security protocol(s) available to gRPC, which means that changes to the security provider after the first channel is created will not be picked up by gRPC.

If depending on Play Services is not an option for your app, then you may bundle Conscrypt with your application. Binaries are available on Maven Central.

Like the Play Services Dynamic Security Provider, you must still "install" Conscrypt before use.

import org.conscrypt.Conscrypt;
import java.security.Security;
...

Security.insertProviderAt(Conscrypt.newProvider(), 1);

JDK versions prior to Java 9 do not support ALPN and are either missing AES GCM support or have 2% the performance of OpenSSL.

We recommend most users use grpc-netty-shaded, which includes netty-tcnative on BoringSSL. It includes pre-built libraries for 64 bit Windows, OS X, and 64 bit Linux. For 32 bit Windows, Conscrypt is an option. For all other platforms, Java 9+ is required.

For users of grpc-netty we recommend netty-tcnative with BoringSSL, although using the built-in JDK support in Java 9+, Conscrypt, and netty-tcnative with OpenSSL are other valid options.

Netty TCNative is a fork of Apache Tomcat's tcnative and is a JNI wrapper around OpenSSL/BoringSSL/LibreSSL.

We recommend BoringSSL for its simplicitly and low occurrence of security vulnerabilities relative to OpenSSL. BoringSSL is used by Conscrypt as well.

Netty-tcnative with BoringSSL includes BoringSSL statically linked in the binary. This means the system's pre-installed TLS libraries will not be used. Production systems that have centralized upgrade agility in the face of security vulnerabilities may want to use netty-tcnative on OpenSSL instead.

Users of grpc-netty-shaded will automatically use netty-tcnative with BoringSSL.

grpc-netty users will need to add the appropriate netty-tcnative-boringssl-static artifact to the application's classpath. Artifacts are available for 64 bit Windows, OS X, and 64 bit Linux.

Depending on netty-tcnative-boringssl-static will include binaries for all supported platforms. For Maven:

  <dependencies>
    <dependency>
      <groupId>io.netty</groupId>
      <artifactId>netty-tcnative-boringssl-static</artifactId>
      <version>2.0.20.Final</version> <!-- See table for correct version -->
      <scope>runtime</scope>
    </dependency>
  </dependencies>

And for Gradle:

dependencies {
  // See table for correct version
  runtime 'io.netty:netty-tcnative-boringssl-static:2.0.20.Final'
}

For projects sensitive to binary size, specify the classifier for the precise platform you need: windows-x86_64, osx-x86_64, linux-x86_64. You can also use os-maven-plugin or osdetector-gradle-plugin, to choose the classifier for the platform running the build.

Using OpenSSL can have more initial configuration issues, but can be useful if your OS's OpenSSL version is recent and kept up-to-date with security fixes. OpenSSL is not included with tcnative, but instead is dynamically linked using your operating system's OpenSSL.

To use OpenSSL you will use the netty-tcnative artifact. It requires:

1. OpenSSL version >= 1.0.2 for ALPN support.
2. Apache APR library (libapr-1) version >= 1.5.2.

You must specify a classifier for the correct netty-tcnative binary: windows-x86_64, osx-x86_64, linux-x86_64, or linux-x86_64-fedora. Fedora derivatives use a different soname from other Linux distributations, so you must select the "fedora" version on those distributions.

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>2.0.20.Final</version> <!-- see table for correct version -->
      <classifier>${tcnative.classifier}</classifier>
      <scope>runtime</scope>
    </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>1.6.2</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>

And in Gradle you can use the osdetector-gradle-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 {
    runtime 'io.netty:netty-tcnative:2.0.20.Final:' + tcnative_classifier
}

Conscrypt provides an implementation of the JSSE security APIs based on BoringSSL. Pre-built binaries are available for 32 and 64 bit Windows, OS X, and 64 bit Linux.

Depend on conscrypt-openjdk-uber for binaries of all supported JRE platforms. For projects sensitive to binary size, depend on conscrypt-openjdk and specify the appropriate classifier. os-maven-plugin and osdetector-gradle-plugin may also be used. See the documentation for netty-tcnative-boringssl-static for example usage of the plugins.

Generally you will "install" Conscrypt before use, for gRPC to find.

import org.conscrypt.Conscrypt;
import java.security.Security;
...

// Somewhere in main()
Security.insertProviderAt(
    Conscrypt.newProviderBuilder().provideTrustManager(false).build(), 1);

Note: according to Conscrypt Implementation Notes, its default HostnameVerifier on OpenJDK always fails. This can be worked around by disabling its default TrustManager implementation as shown above.

Please do not use Jetty ALPN

gRPC historically supported Jetty ALPN for ALPN on Java 8. While functional, it suffers from poor performance and breakages when the JRE is upgraded. When mis-matched to the JRE version, it can also produce unpredictable errors that are hard to diagnose. When using it, it became common practice that any time we saw a TLS failure that made no sense we would blame a Jetty ALPN/JRE version mismatch and we were overwhelmingly correct. The Jetty ALPN agent makes it much easier to use, but we still strongly discourage Jetty ALPN's use.

When using Jetty ALPN with Java 8, realize that performance will be 2-10% that of the other options due to a slow AES GCM implementation in Java.

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(clientCAsFile)
        .clientAuth(ClientAuth.REQUIRE)
        .build());

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

// The application uses this in its handlers
public final static Context.Key<SSLSession> SSL_SESSION_CONTEXT = Context.key("SSLSession");

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

If you received an error message "ALPN is not configured properly" or "Jetty ALPN/NPN has not been properly configured", it most likely means that:

• ALPN related dependencies are either not present in the classpath
• or that there is a classpath conflict
• or that a wrong version is used due to dependency management
• or you are on an unsupported platform (e.g., 32-bit OS). See Transport Security for supported platforms.

If you aren't using gRPC on Android devices, you are most likely using grpc-netty transport.

If you are developing for Android and have a dependency on grpc-netty, you should remove it as grpc-netty is unsupported on Android. Use grpc-okhttp instead.

If you are on a 32-bit operating system, using Java 11+ may be the easiest solution, as ALPN was added to Java in Java 9. If on 32-bit Windows, Conscrypt is an option. Otherwise you need to build your own 32-bit version of netty-tcnative.

If on Alpine Linux and you see "Error loading shared library libcrypt.so.1: No such file or directory". Run apk update && apk add libc6-compat to install the necessary dependency.

If on Alpine Linux, try to use grpc-netty-shaded instead of grpc-netty or (if you need grpc-netty) netty-tcnative-boringssl-static instead of netty-tcnative. If those are not an option, you may consider using netty-tcnative-alpine.

If on Fedora 30 or later and you see "libcrypt.so.1: cannot open shared object file: No such file or directory". Run dnf -y install libxcrypt-compat to install the necessary dependency.

If you are running inside of an embedded Tomcat runtime (e.g., Spring Boot), then some versions of netty-tcnative-boringssl-static will have conflicts and won't work. You must use gRPC 1.4.0 or later.

Most dependency versioning problems can be solved by using io.grpc:grpc-netty-shaded instead of io.grpc:grpc-netty, although this also limits your usage of the Netty-specific APIs. io.grpc:grpc-netty-shaded includes the proper version of Netty and netty-tcnative-boringssl-static in a way that won't conflict with other Netty usages.

Find the dependency tree (e.g., mvn dependency:tree), and look for versions of:

• io.grpc:grpc-netty
• io.netty:netty-handler (really, make sure all of io.netty except for netty-tcnative has the same version)
• io.netty:netty-tcnative-boringssl-static:jar

If netty-tcnative-boringssl-static is missing, then you either need to add it as a dependency, or use alternative methods of providing ALPN capability by reading the Transport Security (TLS) section carefully.

If you have both netty-handler and netty-tcnative-boringssl-static dependencies, then check the versions carefully. These versions could've been overridden by dependency management from another BOM. You would receive the "ALPN is not configured properly" exception if you are using incompatible versions.

If you have other netty dependencies, such as netty-all, that are pulled in from other libraries, then ultimately you should make sure only one netty dependency is used to avoid classpath conflict. The easiest way is to exclude transitive Netty dependencies from all the immediate dependencies, e.g., in Maven use <exclusions>, and then add an explict Netty dependency in your project along with the corresponding tcnative versions. See the versions table below.

If you are running in a runtime environment that also uses Netty (e.g., Hadoop, Spark, Spring Boot 2) and you have no control over the Netty version at all, then you should use a shaded gRPC Netty dependency to avoid classpath conflicts with other Netty versions in runtime the classpath:

• Remove io.grpc:grpc-netty dependency
• Add io.grpc:grpc-netty-shaded dependency

Below are known to work version combinations:

(grpc-netty-shaded avoids issues with keeping these versions in sync.)

If you are using gRPC on Android devices, you are most likely using grpc-okhttp transport.

Find the dependency tree (e.g., mvn dependency:tree), and look for versions of:

• io.grpc:grpc-okhttp
• com.squareup.okhttp:okhttp

If you don't have grpc-okhttp, you should add it as a dependency.

If you have both io.grpc:grpc-netty and io.grpc:grpc-okhttp, you may also have issues. Remove grpc-netty if you are on Android.

If you have okhttp version below 2.5.0, then it may not work with gRPC.

It is OK to have both okhttp 2.x and 3.x since they have different group name and under different packages.

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("dns:///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);