Awesome

ModernHttpClient

Available on NuGet: https://www.nuget.org/packages/modernhttpclient-updated/

This library brings the latest platform-specific networking libraries to Xamarin applications via a custom HttpClient handler.

This is made possible by:

On iOS, NSURLSession
On Android, via OkHttp3
On UWP, via a custom HttpClientHandler.

How can I use this from shared code?

Just reference ModernHttpClient in your .Net Standard or Portable Library, and it will use the correct version on all platforms.

What's new?

Introducing two pinning modes:

CertificateOnly (default)
PublicKeysOnly: used if at least pins for one domain are provided (sha256, sha1 and md5 public keys are supported).

Enabling TLS in pre-Lollipop devices

Install Xamarin.GooglePlayServices.SafetyNet and in your MainActivity:

if (Build.VERSION.SdkInt < BuildVersionCodes.Lollipop)
{
    // Support TLS1.2 on Android versions before Lollipop
    ProviderInstaller.InstallIfNeeded(Application.Context);
}

TLS 1.2+ has been enforced.

Read why here:

https://www.brillianceweb.com/resources/answers-to-7-common-questions-about-upgrading-to-tls-1.2/

Usage

Use TLSConfig parameter to provide server certificate chain public keys and a client certificate for Mutual TLS Authentication.

readonly static HttpClient client = new HttpClient(new NativeMessageHandler(false, new TLSConfig()
{
    Pins = new List<Pin>()
    {
        new Pin()
        {
            Hostname = "*.co.in",
            PublicKeys = new []
            {
                "sha256/MCBrX+0kgfNc/qacknAJ5nojbFIx7kBSJSmXKjJviIg=",
                "sha256/YLh1dUR9y6Kja30RrAn7JKnbQG/uEtLMkBgFF2Fuihg=",
                "sha256/Vjs8r4z+80wjNcr1YKepWQboSIRi63WsWXhIMN+eWys="
            }
        }
    },
    ClientCertificate = new ClientCertificate()
    {
        RawData = "PFX_DATA",
        Passphrase = "PFX_PASSPHRASE"
    }
})
{
    DisableCaching = true,
    Timeout = new TimeSpan(0, 0, 9)
});

Wildcard pattern rules

Asterisk * is only permitted in the left-most domain name label and must be the only character in that label (i.e., must match the whole left-most label).

For example, .example.com is permitted, while a.example.com, a.example.com, ab.example.com, a.*.example.com are not permitted.

Asterisk * cannot match across domain name labels.

For example, *.example.com matches test.example.com but does not match sub.test.example.com.

Wildcard patterns for single-label domain names are not permitted.

Skip pinning for specific domain with empty pins array

readonly static HttpClient client = new HttpClient(new NativeMessageHandler(false, new TLSConfig()
{
    Pins = new List<Pin>()
    {
        new Pin()
        {
            Hostname = "*.co.in",
            PublicKeys = new []
            {
                "sha256/MCBrX+0kgfNc/qacknAJ5nojbFIx7kBSJSmXKjJviIg=",
                "sha256/YLh1dUR9y6Kja30RrAn7JKnbQG/uEtLMkBgFF2Fuihg=",
                "sha256/Vjs8r4z+80wjNcr1YKepWQboSIRi63WsWXhIMN+eWys="
            }
        },
        new Pin()
        {
            Hostname = "example.com",
            PublicKeys = new []{} // Skip pinning for specific domain with empty pins array
        }
    },
    ClientCertificate = new ClientCertificate()
    {
        RawData = "PFX_DATA",
        Passphrase = "PFX_PASSPHRASE"
    }
})
{
    DisableCaching = true,
    Timeout = new TimeSpan(0, 0, 9)
});

How to obtain server certificate chain public keys?

In your Android project add Square.OkHttp3 Nuget Package.
In your Main Activity, add a button and on its click event run this code:

var hostname = "gorest.co.in";
var certificatePinner = new Square.OkHttp3.CertificatePinner.Builder()
    .Add(hostname, "sha256/AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA=")
    .Build();
var client = new OkHttpClient.Builder()
    .CertificatePinner(certificatePinner)
    .Build();
 
var request = new Request.Builder()
    .Url("https://" + hostname)
    .Build();
 
var call = client.NewCall(request);
var response = await call.ExecuteAsync();

As expected, this fails with a certificate pinning exception:

Certificate pinning failure!
  Peer certificate chain:
    sha256/MCBrX+0kgfNc/qacknAJ5nojbFIx7kBSJSmXKjJviIg=: CN=gorest.co.in
    sha256/YLh1dUR9y6Kja30RrAn7JKnbQG/uEtLMkBgFF2Fuihg=: CN=Let's Encrypt Authority X3,O=Let's Encrypt,C=US
    sha256/Vjs8r4z+80wjNcr1YKepWQboSIRi63WsWXhIMN+eWys=: CN=DST Root CA X3,O=Digital Signature Trust Co.
  Pinned certificates for gorest.co.in:
    sha256/AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA=

Follow up by pasting the public key hashes from the exception into the NativeMessageHandler certificate pinner's configuration.

Client certificate as Base64

A certificate in pfx format can be created from client.crt, server.key and a passphrase using openssl:

openssl pkcs12 -export -out client.pfx -inkey server.key -in client.crt

A client.crt can be created following this tutorial: https://gist.github.com/mtigas/952344

The pfx certificate can be converted to Base64 using PowerShell:

$fileContentBytes = get-content 'path-to\client.pfx' -Encoding Byte
[System.Convert]::ToBase64String($fileContentBytes) | Out-File 'path-to\pfx-bytes.txt'

Or, from a terminal window on a Mac:

base64 -i path-to/client.pfx -o path-to/pfx-bytes.txt

How to use NativeCookieHandler?

SetCookie before making the http call and they will be added to Cookie header in the native client:

NativeCookieHandler cookieHandler = new NativeCookieHandler();

readonly static HttpClient client = new HttpClient(new NativeMessageHandler(false, new TLSConfig()
{
    Pins = new List<Pin>()
    {
        new Pin()
        {
            Hostname = "*.co.in",
            PublicKeys = new []
            {
                "sha256/MCBrX+0kgfNc/qacknAJ5nojbFIx7kBSJSmXKjJviIg=",
                "sha256/YLh1dUR9y6Kja30RrAn7JKnbQG/uEtLMkBgFF2Fuihg=",
                "sha256/Vjs8r4z+80wjNcr1YKepWQboSIRi63WsWXhIMN+eWys="
            }
        }
    },
    ClientCertificate = new ClientCertificate()
    {
        RawData = "PFX_DATA",
        Passphrase = "PFX_PASSPHRASE"
    }
},
cookieHandler)
{
    DisableCaching = true,
    Timeout = new TimeSpan(0, 0, 9)
});

var cookie = new Cookie("cookie1", "value1", "/", "reqres.in");
cookieHandler.SetCookie(cookie);

var response = await client.GetAsync(new Uri("https://reqres.in"));

NativeCookieHandler methods

SetCookies(IEnumerable<Cookie> cookies): set native cookies

DeleteCookies(): delete all native cookies.

SetCookie(Cookie cookie): set a native cookie.

DeleteCookie(Cookie cookie): delete a native cookie.

How to use a Web Proxy?

Just provide the Web Proxy configuration as part of the ctor:

readonly static HttpClient client = new HttpClient(new NativeMessageHandler(false, new TLSConfig()
{
    Pins = new List<Pin>()
    {
        new Pin()
        {
            Hostname = "*.co.in",
            PublicKeys = new []
            {
                "sha256/MCBrX+0kgfNc/qacknAJ5nojbFIx7kBSJSmXKjJviIg=",
                "sha256/YLh1dUR9y6Kja30RrAn7JKnbQG/uEtLMkBgFF2Fuihg=",
                "sha256/Vjs8r4z+80wjNcr1YKepWQboSIRi63WsWXhIMN+eWys="
            }
        }
    },
    ClientCertificate = new ClientCertificate()
    {
        RawData = "PFX_DATA",
        Passphrase = "PFX_PASSPHRASE"
    }
},
cookieHandler,
new System.Net.WebProxy("127.0.0.1:80", false))
{
    DisableCaching = true,
    Timeout = new TimeSpan(0, 0, 9)
});

If the Web Proxy address is not reachable, you will get the following exceptions:

iOS:

KCFErrorDomainCFNetwork error 310: cannot find the proxy server.

Android:

System.Net.Http.HttpRequestException
Failed to connect to /127.0.0.1:80

UWP:

Exception: The text associated with this error code could not be found.
The server name or address could not be resolved

Dangerous Zone

Set TLSConfig DangerousAcceptAnyServerCertificateValidator to true, particularly in test scenarios, to connect to a server with a certificate that shouldn't be validated, such as a self-signed certificate.

As a side benefit, developers can use this property to make it easier for tools to flag the danger of disabling certificate validation, which makes it easier for developers to avoid shipping insecure applications.

https://docs.microsoft.com/en-us/dotnet/api/system.net.http.httpclienthandler.dangerousacceptanyservercertificatevalidator?view=netframework-4.8

Enabling CLEARTEXT traffic:

Android

In Android Sdk < Lollipop, CLEARTEXT traffic is enabled by default. In Lollipop and above it needs to be enabled in the AndroidManifest.xml file.

Change the cleartextTrafficPermitted to true in manifest:

<?xml version="1.0" encoding="utf-8"?>
<manifest ...>
    <uses-permission android:name="android.permission.INTERNET" />
    <application
        ...
        android:usesCleartextTraffic="true"
        ...>
        ...
    </application>
</manifest>

This may appear to fix the problem but it opens a threat to data integrity.

Adding Network Security Config xml file in manifest:

Create the Network security config.xml in resource xml folder

<?xml version="1.0" encoding="utf-8"?>
<network-security-config>
    <domain-config cleartextTrafficPermitted="true">
        <domain includeSubdomains="true">your.domain.com</domain>
    </domain-config>
</network-security-config>

Add the Network security config.xml in manifest like following

<application
    android:name=".MyApplication"
    android:networkSecurityConfig="@xml/network_security_config"
... />

iOS

Adding NSAppTransportSecurity NSExceptionDomains at info.plist:

<key>NSAppTransportSecurity</key>
<dict>
    <key>NSExceptionDomains</key>
    <dict>
        <key>gorest.co.in</key>
        <dict>
            <key>NSExceptionAllowsInsecureHTTPLoads</key>
            <true/>
        </dict>
    </dict>
</dict>

Note: better use a secure network traffic rather than cleartext.

Release Notes

3.4.2

[Android] Deprecating DangerousAllowInsecureHTTPLoads

[Android] CLEARTEXT enabled by default in pre-Lollipop

[Update] Refactoring CertificatePinner to match Android OkHttp

[Update] Adding CertificateOnly and PublicKeysOnly pinning modes

[Update] Default pinning mode set to CertificateOnly

[Update] Pinning mode set to PublicKeysOnly if at least pins for one domain are provided

[Update] MatchHostnameToPattern applied to all alternative names when validating hostname

[Update] Performing cookie path-checking before adding them to the cookie collection (PR by @phdonnelly)

[Update] Supporting public keys in sha256, sha1 and md5 formats

3.3.4

[Update] Skip pinning for specific domain with empty pins array

[Update] Validating pins and client certificate base64 string

3.3.3

[Update] Adding support for Proxy-Authorization

[UWP] Pin wildcard hostnames #34

3.3.2

[Android] Supporting TLS 1.2+

3.3.1

[Android] Allowing TLS with CLEARTEXT simultaneously

3.3.0

Renaming SSLConfig to TLSConfig

Renaming EnableUntrustedCertificates to DangerousAcceptAnyServerCertificateValidator, moving it as a property of TLSConfig

Adding TLSConfig DangerousAllowInsecureHTTPLoads to enable plaintext HTTP in Android, matching iOS NSAppTransportSecurity $35

Adding support for wildcard hostname validation #34

3.2.1

Cumulative versioning update

2.8.2

[Update] Validating hostname against certificate Subject Alternative Names, if any, in case it doesn't match the CN

2.8.1

[iOS] Timeout using wrong TimeSpan value #31.

[Android] "Trust anchor for certification path not found." with self-signed certificate.

2.8.0

Code refactoring.

Adding support for Mutual TLS Authentication

Enforcing TLS1.2

Adding support for web proxy.

[iOS] Removing minimumSSLProtocol static property.

[Android] Removing verifyHostnameCallback static property.

[Android] Removing customTrustManager static property.

2.7.2

[Android] Handshake failed (adding customTrustManager static property) #11

2.7.1

[Android] MissingMethodException Method 'ModernHttpClient.NativeMessageHandler..ctor' not found. #9

[iOS] Removing minimumSSLProtocol from NativeMessageHandler ctor

[UWP] Exception on UWP with Xamarin Forms #3

2.7.0

[Update] Migrating to a multi-target project

[Android] Calling HttpClient methods should throw .Net Exception when fail #5

[Android] VerifyHostnameCallback parameter function on constructor (NativeMessageHandler - Android) when customSSLVerification is true #6

[Android] ReasonPhrase is empty under HTTPS #8

2.6.0

[Update] Adding support for UWP

[Update] Adding support for netstandard 2.0

2.5.3

[Update] Cookies set with the native handler will be merged into the Cookie header

2.5.1

[Android] NativeCookieHandler, if provided, is set as the default CookieJar for OkHttpClient

[Update] Adding DeleteCookies, SetCookie and DeleteCookie to NativeCookieHandler

2.5.0

[Android] Updating to Square.OkHttp3

2.4.9

[Android] Calling HttpClient methods should throw .Net Exception when fail #5

[Android] MissingMethodException Method 'ModernHttpClient.NativeMessageHandler..ctor' not found. #9

[Android] VerifyHostnameCallback parameter function on constructor when customSSLVerification is true #6

[Android] ReasonPhrase is empty under HTTPS #8

[Android] Handshake failed (adding customTrustManager static property) #11

[iOS] Removing minimumSSLProtocol from NativeMessageHandler ctor

2.4.7

[Update] Cookies set with the native handler will be merged into the Cookie header

2.4.5

[Android] NativeCookieHandler, if provided, is set as the default cookie handler for OkHttpClient

[Update] Adding DeleteCookies, SetCookie and DeleteCookie to NativeCookieHandler

2.4.4

[Android] SIGABRT after UnknownHostException #229

[iOS] Updating obsolete NSUrlSessionDelegate to INSUrlSessionDelegate

[Update] Adding EnableUntrustedCertificates to support self-signed certificates

2.4.3

[Update] Adding Timeout property

[Android] Updating to Square.OkHttp 2.7.5

[Android] Timeout value is not respected on Android #192