HttpRequestAdapter.java

package com.f2prateek.five00px.data.api.auth;

import java.io.IOException;
import java.io.InputStream;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.Map;
import oauth.signpost.http.HttpRequest;
import retrofit.client.Header;
import retrofit.client.Request;

public class HttpRequestAdapter implements HttpRequest {
  private static final String DEFAULT_CONTENT_TYPE = "application/json";

  private Request request;
  private String contentType;

  public HttpRequestAdapter(Request request) {
    this(request, DEFAULT_CONTENT_TYPE);
  }

  public HttpRequestAdapter(Request request, String contentType) {
    this.request = request;
    this.contentType = contentType;
  }

  @Override
  public Map<String, String> getAllHeaders() {
    HashMap<String, String> headers = new HashMap<String, String>();
    for (Header header : request.getHeaders()) {
      headers.put(header.getName(), header.getValue());
    }
    return headers;
  }

  @Override
  public String getContentType() {
    return contentType;
  }

  @Override
  public String getHeader(String key) {
    for (Header header : request.getHeaders()) {
      if (key.equals(header.getName())) {
        return header.getValue();
      }
    }
    return null;
  }

  @Override
  public InputStream getMessagePayload() throws IOException {
    throw new RuntimeException(new UnsupportedOperationException());
  }

  @Override
  public String getMethod() {
    return request.getMethod();
  }

  @Override
  public String getRequestUrl() {
    return request.getUrl();
  }

  @Override
  public void setHeader(String key, String value) {
    ArrayList<Header> headers = new ArrayList<Header>();
    headers.addAll(request.getHeaders());
    headers.add(new Header(key, value));
    Request copy = new Request(request.getMethod(), request.getUrl(), headers, request.getBody());
    request = copy;
  }

  @Override
  public void setRequestUrl(String url) {
    throw new RuntimeException(new UnsupportedOperationException());
  }

  @Override
  public Object unwrap() {
    return request;
  }
}

RetrofitHttpOAuthConsumer.java

package com.f2prateek.five00px.data.api.auth;

import oauth.signpost.AbstractOAuthConsumer;
import oauth.signpost.http.HttpRequest;
import retrofit.client.Request;

public class RetrofitHttpOAuthConsumer extends AbstractOAuthConsumer {
  private static final long serialVersionUID = 1L;

  public RetrofitHttpOAuthConsumer(String consumerKey, String consumerSecret) {
    super(consumerKey, consumerSecret);
  }

  @Override
  protected HttpRequest wrap(Object request) {
    if (!(request instanceof retrofit.client.Request)) {
      throw new IllegalArgumentException("This consumer expects requests of type "
          + retrofit.client.Request.class.getCanonicalName());
    }
    return new HttpRequestAdapter((Request) request);
  }
}

SigningOkClient.java

package com.f2prateek.five00px.data.api.auth;

import com.f2prateek.ln.Ln;
import java.io.IOException;
import oauth.signpost.OAuthConsumer;
import oauth.signpost.exception.OAuthCommunicationException;
import oauth.signpost.exception.OAuthExpectationFailedException;
import oauth.signpost.exception.OAuthMessageSignerException;
import retrofit.client.OkClient;
import retrofit.client.Request;
import retrofit.client.Response;

/**
 * This is a helper class, a {@code retrofit.client.UrlConnectionClient} to use
 * when building your {@code retrofit.RestAdapter}.
 */
public class SigningOkClient extends OkClient {
  private final OAuthConsumer consumer;

  public SigningOkClient(OAuthConsumer consumer) {
    this.consumer = consumer;
  }

  @Override
  public Response execute(Request request) throws IOException {
    Request requestToSend = request;
    try {
      HttpRequestAdapter signedAdapter = (HttpRequestAdapter) consumer.sign(request);
      requestToSend = (Request) signedAdapter.unwrap();
    } catch (OAuthMessageSignerException | OAuthExpectationFailedException | OAuthCommunicationException e) {
      Ln.e(e);
    }
    return super.execute(requestToSend);
  }
}