java.util.zip.ZipException: duplicate entry: AbstractHttpContent.class

I'm getting the duplicate entry error for abstractHttpContent.class which is part of app engine.

I'm using google app engine backend. I also have multidex enabled, without multidex it give me an method exceeded error.

here is my app gradle file

apply plugin: 'com.android.application'
apply plugin: 'com.google.gms.google-services'

android {
    compileSdkVersion 23
    buildToolsVersion "23.0.2"


    defaultConfig {
        applicationId "com.example.joseph.googlesign_in"
        minSdkVersion 16
        targetSdkVersion 23
        versionCode 1
        versionName "1.0"
        multiDexEnabled true
    }

    dexOptions {
        javaMaxHeapSize "4g"
    }

    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
}


dependencies {
    compile fileTree(dir: 'libs', include: ['*.jar'])
    testCompile 'junit:junit:4.12'
    compile 'com.android.support:appcompat-v7:23.1.1'
    compile 'com.google.android.gms:play-services-auth:8.3.0'
    compile project(path: ':gsiBackend', configuration: 'android-endpoints')
    compile project(':gsiBackend')
}

Here is my backend gradle file

buildscript {
    repositories {
        jcenter()
    }
    dependencies {
        classpath 'com.google.appengine:gradle-appengine-plugin:1.9.18'
    }
}

repositories {
    jcenter();
}

apply plugin: 'java'
apply plugin: 'war'
apply plugin: 'appengine'

sourceCompatibility = JavaVersion.VERSION_1_7
targetCompatibility = JavaVersion.VERSION_1_7

dependencies {
    appengineSdk 'com.google.appengine:appengine-java-sdk:1.9.18'
    compile 'com.google.appengine:appengine-endpoints:1.9.18'
    compile 'com.google.appengine:appengine-endpoints-deps:1.9.18'
    compile 'javax.servlet:servlet-api:2.5'
}

appengine {
    downloadSdk = true
    appcfg {
        oauth2 = true
    }
    endpoints {
        getClientLibsOnBuild = true
        getDiscoveryDocsOnBuild = true
    }
}

The location of abstractHttpContent.class

It seems the error started after adding google play services to use google sign in.
Has anyone encountered this build error? Any advice on how to fix it?
Thanks