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CWAC-NetSecurity: Simplifying Secure Internet Access

This library contains a backport of the Android 7.0 network security configuration subsystem. In Android 7.0, this subsystem makes it easier for developers to tie their app to particular certificate authorities or certificates, support self-signed certificates, and handle other advanced SSL certificate scenarios. This backport allows the same XML configuration to be used, going back to API Level 17 (Android 4.2).

This library also offers a TrustManagerBuilder and related classes to make it easier for developers to integrate the network security configuration backport, particularly for OkHttp3 and HttpURLConnection.

This library also includes support for certificate memorization, where you can elect to trust certificates discovered "in the wild", either automatically or with user approval.

Note that OkHttp has its own CertificatePinner. If all you are looking to do is pin certificates, and you are usign OkHttp (and you should be!), use CertificatePinner and do not use CWAC-NetSecurity. Conversely, if there are advanced features of CWAC-NetSecurity that you wish to use, that's great... but do not also use CertificatePinner. Use one or the other, not both.

Installation

The artifact for this library is distributed via the CWAC repository, so you will need to configure that in your module's build.gradle file, along with your compile statement:

repositories {
    maven {
        url "https://s3.amazonaws.com/repo.commonsware.com"
    }
}

dependencies {
    implementation 'com.commonsware.cwac:netsecurity:0.5.0'
    implementation 'com.squareup.okhttp3:okhttp:3.9.1'
}

If you are using this library with OkHttp3, you also need to have an implementation statement for a compatible OkHttp3 artifact, as shown above. Right now, the most recent compatible OkHttp3 version is 3.9.1.

If you are using HttpURLConnection, or tying this code into some other HTTP client stack, you can skip the OkHttp3 dependency.

Basic Usage

Start by following Google's documentation for the Android 7.0 network security configuration. Ideally, confirm that your configuration works using an Android 7.0+ device.

Next, add in this <meta-data> element to your manifest, as a child of the <application> element:

<meta-data
  android:name="android.security.net.config"
  android:resource="@xml/net_security_config" />

The value for android:resource should be the same XML resource that you used in the android:networkSecurityConfig attribute in the <application> element.

Then, in your code where you want to set up your network communications, create a TrustManagerBuilder and teach it to load the configuration from the manifest:

TrustManagerBuilder tmb=
  new TrustManagerBuilder().withManifestConfig(ctxt);

(where ctxt is some Context)

If you are using OkHttp3, create your basic OkHttpClient.Builder, then call:

OkHttp3Integrator.applyTo(tmb, okb);

(where tmb is the TrustManagerBuilder from before, and okb is your OkHttpClient.Builder)

At this point, you can create your OkHttpClient from the Builder and start using it.

If you are using HttpURLConnection, you can call applyTo() on the TrustManagerBuilder itself, passing in the HttpURLConnection. Afterwards, you can start using the HttpURLConnection to make your HTTP request.

In either case, on Android 7.0+ devices, withManifestConfig() will not use the backport. Instead, the platform-native implementation of the network security configuration subsystem will be used. On Android 4.2-6.0 devices, the backport will be used.

Basic Limitations

If you use HttpURLConnection, you cannot use <domain-config> elements in the network security configuration XML. Similarly, you cannot use cleartextTrafficPermitted with HttpURLConnection. If you have them in the XML, they will be ignored.

OkHttp3 should support the full range of network security configuration XML features.

The <certificates src="user" /> cannot really be supported prior to Android 7.0, insofar as the system will check user certificates any time it checks for system certificates. If you include such an element in a configuration:

  • If you are using withManifestConfig(), a warning will be logged to LogCat, and the element will be treated as if it were <certificates src="system" />

  • If you are using anything else (e.g., withConfig()), your app will crash at startup, with an error indicating that <certificates src="user" /> is not supported

Advanced Usage

If you want to employ certificate memorization or otherwise do more sophisticated things with the network security configuration backport and/or TrustManagerBuilder, there is a separate page of documentation for that.

Notes for Upgraders

If you are upgrading to v0.3.0 or higher from v0.2.1 or older, and you are using <certificates src="user" />, note that this is no longer supported (see above).

Compiling from Source and Running the Test Suites

The instrumentation tests in androidTest/ are divided into two sub-packages: pub and priv.

The pub tests hit publicly-available Web servers (mostly those hosted by CommonsWare). As such, you should be able to run those tests without issue.

The priv tests need additional configuration on your part. That configuration is designed to be held in a gradle.properties file that you need to add to your root directory of your copy of the project code. Specifically, three values should reside there:

  • TEST_PRIVATE_HTTP_URL: a URL to some Web server that you control
  • TEST_PRIVATE_HTTPS_URL: a URL to some Web server that you control, where the communications are secured via SSL using a self-signed certificate
  • TEST_PRIVATE_HTTP_REDIR_URL: a URL to some Web server that you control that, when requested, issues a server-side redirect to an SSL-secured page (such as the one from TEST_PRIVATE_HTTPS_URL)

The first two URLs should each return:

{"Hello": "world"}

You will need to define those values in your gradle.properties file even if you are just planning on modifying the code, as otherwise the build.gradle files for the library modules will fail, as they expect those values.

In addition, if you wish to run the priv tests, you will need to replace the androidTest/res/raw/selfsigned.crt file in each library module with the CRT file that matches your self-signed certificate that TEST_PRIVATE_HTTPS_URL uses.

Note that right now the tests require Android 8.1 or older; some tests will not work on Android 9.0 and higher.

Dependencies

netsecurity has a provided dependency on OkHttp3. Version 0.5.0 of this library uses OkHttp version 3.9.1. netsecurity presently is not compatible with newer versions of OkHttp.

Otherwise, there are no external dependencies.

Version

The current version is 0.5.0.

License

All of the code in this repository is licensed under the Apache Software License 2.0. Look to the headers of the Java source files to determine the actual copyright holder, as it is a mix of the Android Open Source Project and CommonsWare, LLC.

Questions

If you have questions regarding the use of this code, please post a question on Stack Overflow tagged with commonsware-cwac and android after searching to see if there already is an answer. Be sure to indicate what CWAC module you are having issues with, and be sure to include source code and stack traces if you are encountering crashes.

If you have encountered what is clearly a bug, or if you have a feature request, please read the contribution guidelines, then post an issue. Be certain to include complete steps for reproducing the issue. If you believe that the issue you have found represents a security bug, please follow the instructions in the contribution guidelines.

You are also welcome to join the CommonsWare Community and post questions and ideas to the CWAC category.

Do not ask for help via social media.

AOSP Version Tracking and Release Notes

Library Version AOSP Code Base Release Notes
v0.5.0 Android 9.0 source code from the SDK, plus the android-7.1.0_r7 tagged edition of conscrypt updated to OkHttp 3.9.1 and newer build instructions, added methods to CompositeTrustManager
v0.4.5 Android 8.0 source code from the SDK, plus the android-7.1.0_r7 tagged edition of conscrypt updated to OkHttp 3.9.0 and newer Android Plugin for Gradle, Gradle
v0.4.4 Android 7.1 source code from the SDK, plus the android-7.1.0_r7 tagged edition of conscrypt updated to OkHttp 3.8.1 and fixed testing bug
v0.4.3 Android 7.1 source code from the SDK, plus the android-7.1.0_r7 tagged edition of conscrypt updated to OkHttp 3.8.0 and new test SSL certificate
v0.4.2 Android 7.1 source code from the SDK, plus the android-7.1.0_r7 tagged edition of conscrypt added single-item-chain filtering for memorization
v0.4.1 Android 7.1 source code from the SDK, plus the android-7.1.0_r7 tagged edition of conscrypt switched to OkHttp 3.6.0, add domain filtering for memorization
v0.4.0 Android 7.1 source code from the SDK, plus the android-7.1.0_r7 tagged edition of conscrypt added certificate memorization and NetCipher integration options
v0.3.1 Android 7.1 source code from the SDK, plus the android-7.1.0_r7 tagged edition of conscrypt bug fix per issue #7
v0.3.0 Android 7.1 source code from the SDK, plus the android-7.1.0_r7 tagged edition of conscrypt user validation per issue #5
v0.2.1 Android 7.1 source code from the SDK, plus the android-7.1.0_r7 tagged edition of conscrypt bug fix per issue #3
v0.2.0 Android 7.0 source code from the SDK, plus the android-7.0.0_r1 tagged edition of conscrypt HttpURLConnection no longer requires setHost() call
v0.1.0 Android 7.0 source code from the SDK, plus the android-7.0.0_r1 tagged edition of conscrypt update for new version of Android
v0.0.1 android-n-preview-4 initial release