如何在Android Retrofit的GET/POST请求中通过URL参数实现认证？

我已经在Android项目中基于Retrofit实现了带URL参数形式认证（用户名admin，密码admin）的GET和POST请求，下面是完整的配置与代码实现：

首先需要在AndroidManifest.xml中添加网络权限：

<uses-permission android:name="android.permission.INTERNET" />

在模块级的build.gradle中添加以下依赖：

implementation 'com.android.volley:volley:1.1.0'
implementation 'com.squareup.retrofit2:retrofit:2.3.0'
implementation 'com.squareup.retrofit2:adapter-rxjava2:2.3.0'
implementation 'com.squareup.retrofit2:converter-gson:2.3.0'
implementation 'io.reactivex.rxjava2:rxandroid:2.0.1'
implementation 'com.google.code.gson:gson:2.8.5'

这个类采用单例模式初始化Retrofit实例，确保全局唯一：

public class Api {
    private static final String BASE_URL="https://your_url";
    private static Api instance;
    private final IApiCall iApiCallInterface;
    private Api() {
        Gson gson = new GsonBuilder().setLenient().create();
        final OkHttpClient okHttpClient = new OkHttpClient.Builder()
                .connectTimeout(60, TimeUnit.SECONDS)
                .writeTimeout(60, TimeUnit.SECONDS)
                .readTimeout(60, TimeUnit.SECONDS)
                .build();
        Retrofit retrofit = new Retrofit.Builder().client(okHttpClient).baseUrl(BASE_URL)
                .addCallAdapterFactory(RxJava2CallAdapterFactory.create())
                .addConverterFactory(GsonConverterFactory.create(gson)).build();
        iApiCallInterface = retrofit.create(IApiCall.class);
    }
    public static Api start() {
        return instance = instance == null ? new Api() : instance;
    }
    public Observable<Example> getSendMoneyCountries() {
        return iApiCallInterface.getCategoryList();
    }
}

这里定义了具体的API请求接口，示例为GET请求：

public interface IApiCall {
    //response in in json array
    @Headers("Content-Type: application/json")
    @GET("/json")
    Observable<Example> getCategoryList();
}

在Activity中初始化Api实例并发起请求，借助RxJava完成线程调度：

private static Api api;
api = Api.start();
api.getSendMoneyCountries()
        .subscribeOn(Schedulers.io())
        .observeOn(AndroidSchedulers.mainThread())
        .subscribeWith(new DisposableObserver<Example>() {
            @Override
            public void onNext(Example response) {
                //clear array list
                //response store in array list
            }
            @Override
            public void onError(Throwable e) {
                //show toast msg
            }
            @Override
            public void onComplete() {
                //perform db insertion operation seperate thread
                //check for duplicate
            }
        });

内容的提问来源于stack exchange，提问作者Sagar H