added SignatureType and querystring signing functionallity

src/main/java/org/scribe/model/OAuthConfig.java

@@ -10,6 +10,7 @@ public class OAuthConfig
   private String apiKey;
   private String apiSecret;
   private String callback;
+  private SignatureType signatureType;
   
   public OAuthConfig(String key, String secret)
   {
@@ -52,4 +53,14 @@ public class OAuthConfig
   {
     this.callback = callback;
   }
+
+  public SignatureType getSignatureType()
+  {
+    return signatureType != null ? signatureType : SignatureType.Header;
+  }
+
+  public void setSignatureType(SignatureType type)
+  {
+    this.signatureType = type;
+  }
 }

src/main/java/org/scribe/model/SignatureType.java

@@ -0,0 +1,7 @@
+package org.scribe.model;
+
+public enum SignatureType
+{
+  Header,
+  QueryString
+}

src/main/java/org/scribe/oauth/OAuth10aServiceImpl.java

@@ -1,5 +1,7 @@
 package org.scribe.oauth;
 
+import java.util.*;
+
 import org.scribe.builder.api.*;
 import org.scribe.model.*;
 
@@ -110,7 +112,18 @@ public class OAuth10aServiceImpl implements OAuthService
 
   private void addSignature(OAuthRequest request)
   {
-    String oauthHeader = api.getHeaderExtractor().extract(request);
-    request.addHeader(OAuthConstants.HEADER, oauthHeader);
+    switch (config.getSignatureType())
+    {
+      case Header:
+        String oauthHeader = api.getHeaderExtractor().extract(request);
+        request.addHeader(OAuthConstants.HEADER, oauthHeader);
+        break;
+      case QueryString:
+        for (Map.Entry<String, String> entry : request.getOauthParameters().entrySet())
+        {
+          request.addQuerystringParameter(entry.getKey(), entry.getValue());
+        }
+        break;
+    }
   }
 }