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# Specialized Services
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Custom OAuth service implementations that extend the base OAuth functionality with provider-specific features like additional security measures, custom signature requirements, and specialized token handling.
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## Capabilities
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### Facebook Service
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Facebook-specific OAuth service that adds app secret proof to all authenticated requests for enhanced security.
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```java { .api }
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public class FacebookService extends OAuth20Service {
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    public FacebookService(FacebookApi api, String apiKey, String apiSecret, 
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                          String callback, String defaultScope, String responseType, 
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                          OutputStream debugStream, String userAgent, 
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                          HttpClientConfig httpClientConfig, HttpClient httpClient);
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    public void signRequest(String accessToken, OAuthRequest request);
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}
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```
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The Facebook service automatically adds the `appsecret_proof` parameter to all requests, which is calculated as HMAC-SHA256 of the access token using the app secret as the key.
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**Usage Example:**
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```java
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// FacebookApi automatically creates FacebookService
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OAuth20Service service = new ServiceBuilder("app_id")
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    .apiSecret("app_secret")
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    .callback("callback_url")
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    .build(FacebookApi.instance());
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// When making requests, appsecret_proof is automatically added
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OAuthRequest request = new OAuthRequest(Verb.GET, "https://graph.facebook.com/me");
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service.signRequest(accessToken.getAccessToken(), request);
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// Request will include: appsecret_proof=<hmac_sha256_signature>
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```
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### Instagram Service
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Instagram-specific OAuth service for Instagram API integration.
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```java { .api }
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public class InstagramService extends OAuth20Service {
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    public InstagramService(InstagramApi api, String apiKey, String apiSecret,
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                           String callback, String defaultScope, String responseType,
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                           OutputStream debugStream, String userAgent,
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                           HttpClientConfig httpClientConfig, HttpClient httpClient);
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}
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```
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**Usage Example:**
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```java
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// InstagramApi creates InstagramService automatically
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OAuth20Service service = new ServiceBuilder("client_id")
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    .apiSecret("client_secret")  
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    .callback("callback_url")
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    .build(InstagramApi.instance());
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```
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### Mail.ru OAuth Service
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Mail.ru-specific OAuth service that adds signature parameter for API requests.
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```java { .api }
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public class MailruOAuthService extends OAuth20Service {
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    public MailruOAuthService(MailruApi api, String apiKey, String apiSecret,
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                             String callback, String defaultScope, String responseType,
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                             OutputStream debugStream, String userAgent,
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                             HttpClientConfig httpClientConfig, HttpClient httpClient);
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    public void signRequest(String accessToken, OAuthRequest request);
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}
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```
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The Mail.ru service automatically adds a signature parameter to requests based on Mail.ru's API requirements.
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**Usage Example:**
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```java
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// MailruApi creates MailruOAuthService automatically
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OAuth20Service service = new ServiceBuilder("client_id")
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    .apiSecret("client_secret")
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    .callback("callback_url")
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    .build(MailruApi.instance());
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// Signature is automatically added to requests
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OAuthRequest request = new OAuthRequest(Verb.GET, "https://www.appsmail.ru/platform/api");
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service.signRequest(accessToken.getAccessToken(), request);
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```
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### Polar OAuth Service
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Polar-specific OAuth service for Polar fitness platform integration.
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```java { .api }
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public class PolarOAuthService extends OAuth20Service {
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    public PolarOAuthService(PolarAPI api, String apiKey, String apiSecret,
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                            String callback, String defaultScope, String responseType,
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                            OutputStream debugStream, String userAgent,
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                            HttpClientConfig httpClientConfig, HttpClient httpClient);
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}
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```
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**Usage Example:**
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```java
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// PolarAPI creates PolarOAuthService automatically  
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OAuth20Service service = new ServiceBuilder("client_id")
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    .apiSecret("client_secret")
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    .callback("callback_url")
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    .build(PolarAPI.instance());
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```
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### Wunderlist OAuth Service
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Wunderlist-specific OAuth service for Wunderlist task management integration.
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```java { .api }
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public class WunderlistOAuthService extends OAuth20Service {
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    public WunderlistOAuthService(WunderlistAPI api, String apiKey, String apiSecret,
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                                 String callback, String defaultScope, String responseType,
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                                 OutputStream debugStream, String userAgent,
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                                 HttpClientConfig httpClientConfig, HttpClient httpClient);
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}
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```
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**Usage Example:**
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```java
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// WunderlistAPI creates WunderlistOAuthService automatically
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OAuth20Service service = new ServiceBuilder("client_id")
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    .apiSecret("client_secret")
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    .callback("callback_url")
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    .build(WunderlistAPI.instance());
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```
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### Imgur OAuth Service
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Imgur-specific OAuth service for Imgur image hosting integration.
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```java { .api }
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public class ImgurOAuthService extends OAuth20Service {
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    public ImgurOAuthService(ImgurApi api, String apiKey, String apiSecret,
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                            String callback, String defaultScope, String responseType,
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                            OutputStream debugStream, String userAgent,
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                            HttpClientConfig httpClientConfig, HttpClient httpClient);
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}
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```
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**Usage Example:**
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```java
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// ImgurApi creates ImgurOAuthService automatically
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OAuth20Service service = new ServiceBuilder("client_id")
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    .apiSecret("client_secret")
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    .callback("callback_url")
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    .build(ImgurApi.instance());
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```
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### Odnoklassniki OAuth Service
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Odnoklassniki-specific OAuth service that adds signature parameter for Russian social network API.
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```java { .api }
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public class OdnoklassnikiOAuthService extends OAuth20Service {
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    public OdnoklassnikiOAuthService(OdnoklassnikiApi api, String apiKey, String apiSecret,
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                                    String callback, String defaultScope, String responseType,
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                                    OutputStream debugStream, String userAgent,
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                                    HttpClientConfig httpClientConfig, HttpClient httpClient);
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    public void signRequest(String accessToken, OAuthRequest request);
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}
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```
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The Odnoklassniki service automatically adds a signature parameter to requests based on Odnoklassniki's API security requirements.
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**Usage Example:**
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```java
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// OdnoklassnikiApi creates OdnoklassnikiOAuthService automatically
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OAuth20Service service = new ServiceBuilder("application_key")
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    .apiSecret("secret_key")
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    .callback("callback_url")
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    .build(OdnoklassnikiApi.instance());
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// Signature is automatically added to requests
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OAuthRequest request = new OAuthRequest(Verb.GET, "https://api.odnoklassniki.ru/fb.do");
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service.signRequest(accessToken.getAccessToken(), request);
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```
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## Service Creation
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Specialized services are automatically created when using the corresponding API classes through the `createService()` method override:
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```java { .api }
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// Base API method that specialized APIs override
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public OAuth20Service createService(String apiKey, String apiSecret, String callback,
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                                   String defaultScope, String responseType, 
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                                   OutputStream debugStream, String userAgent,
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                                   HttpClientConfig httpClientConfig, HttpClient httpClient);
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```
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## Key Features
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### Enhanced Security
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- **Facebook**: Adds `appsecret_proof` parameter using HMAC-SHA256 signature
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- **Mail.ru**: Adds signature parameter for API request validation
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- **Odnoklassniki**: Adds signature parameter for Russian API compliance
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### Provider-Specific Handling
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- **Instagram**: Handles Instagram's specific OAuth flow requirements
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- **Polar**: Manages Polar fitness platform's API specifics
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- **Wunderlist**: Handles Wunderlist task management API requirements
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- **Imgur**: Manages Imgur image hosting API specifics
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### Transparent Usage
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All specialized services maintain the same `OAuth20Service` interface, so they can be used exactly like standard OAuth services. The provider-specific functionality is applied automatically when signing requests.
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## Common Pattern
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```java
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// All specialized services follow this pattern:
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OAuth20Service service = new ServiceBuilder("client_id")
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    .apiSecret("client_secret")  
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    .callback("callback_url")
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    .build(SpecializedApi.instance()); // Returns specialized service automatically
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// Standard OAuth flow works the same
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String authUrl = service.getAuthorizationUrl();
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OAuth2AccessToken token = service.getAccessToken("authorization_code");
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// Provider-specific features are applied automatically
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OAuthRequest request = new OAuthRequest(Verb.GET, "https://api.provider.com/endpoint");
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service.signRequest(token.getAccessToken(), request); // Specialized signing applied here
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Response response = service.execute(request);
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```