use String for OAuth requests

Author: paullatzelsperger

spi/common/oauth2-spi/src/main/java/org/eclipse/edc/iam/oauth2/spi/client/Oauth2CredentialsRequest.java

@@ -20,6 +20,8 @@
 import java.util.Map;
 import java.util.Objects;
 
+import static java.util.Optional.ofNullable;
+
 public abstract class Oauth2CredentialsRequest {
 
     private static final String GRANT_TYPE = "grant_type";
@@ -34,21 +36,21 @@ public String getUrl() {
         return url;
     }
 
-    public Object getScope() {
-        return params.get(SCOPE);
+    public String getScope() {
+        return ofNullable(params.get(SCOPE)).map(Object::toString).orElse(null);
     }
 
-    public Object getGrantType() {
-        return params.get(GRANT_TYPE);
+    public String getGrantType() {
+        return ofNullable(params.get(GRANT_TYPE)).map(Object::toString).orElse(null);
     }
 
     /**
      * The audience for which an access token will be requested.
      *
      * @return The value of the resource form parameter.
      */
-    public Object getResource() {
-        return this.params.get(RESOURCE);
+    public String getResource() {
+        return ofNullable(params.get(RESOURCE)).map(Object::toString).orElse(null);
     }
 
     public Map<String, Object> getParams() {

spi/common/oauth2-spi/src/main/java/org/eclipse/edc/iam/oauth2/spi/client/PrivateKeyOauth2CredentialsRequest.java

@@ -18,18 +18,20 @@
 
 import java.util.Objects;
 
+import static java.util.Optional.ofNullable;
+
 public class PrivateKeyOauth2CredentialsRequest extends Oauth2CredentialsRequest {
 
     private static final String CLIENT_ASSERTION = "client_assertion";
     private static final String CLIENT_ASSERTION_TYPE = "client_assertion_type";
     private static final String TYPE_JWT_BEARER = "urn:ietf:params:oauth:client-assertion-type:jwt-bearer";
 
-    public Object getClientAssertion() {
-        return params.get(CLIENT_ASSERTION);
+    public String getClientAssertion() {
+        return ofNullable(params.get(CLIENT_ASSERTION)).map(Object::toString).orElse(null);
     }
 
     public Object getClientAssertionType() {
-        return params.get(CLIENT_ASSERTION_TYPE);
+        return ofNullable(params.get(CLIENT_ASSERTION_TYPE)).map(Object::toString).orElse(null);
     }
 
     public static class Builder<B extends PrivateKeyOauth2CredentialsRequest.Builder<B>> extends Oauth2CredentialsRequest.Builder<PrivateKeyOauth2CredentialsRequest, PrivateKeyOauth2CredentialsRequest.Builder<B>> {