Use a separate library for base64-encoding in the okhttp-gson template

modules/swagger-codegen/src/main/resources/Java/libraries/okhttp-gson/auth/HttpBasicAuth.mustache

@@ -0,0 +1,41 @@
+package {{invokerPackage}}.auth;
+
+import {{invokerPackage}}.Pair;
+
+import com.migcomponents.migbase64.Base64;
+
+import java.util.Map;
+import java.util.List;
+
+import java.io.UnsupportedEncodingException;
+
+public class HttpBasicAuth implements Authentication {
+  private String username;
+  private String password;
+
+  public String getUsername() {
+    return username;
+  }
+
+  public void setUsername(String username) {
+    this.username = username;
+  }
+
+  public String getPassword() {
+    return password;
+  }
+
+  public void setPassword(String password) {
+    this.password = password;
+  }
+
+  @Override
+  public void applyToParams(List<Pair> queryParams, Map<String, String> headerParams) {
+    String str = (username == null ? "" : username) + ":" + (password == null ? "" : password);
+    try {
+      headerParams.put("Authorization", "Basic " + Base64.encodeToString(str.getBytes("UTF-8"), false));
+    } catch (UnsupportedEncodingException e) {
+      throw new RuntimeException(e);
+    }
+  }
+}