revert extraction of oauth server metadata

auth/services/oauth/relying_party.go

@@ -133,9 +133,9 @@ func (s *relyingParty) RequestRFC003AccessToken(ctx context.Context, jwtGrantTok
 
 func (s *relyingParty) RequestRFC021AccessToken(ctx context.Context, requester did.DID, verifier did.DID, scopes string) (*oauth.TokenResponse, error) {
 	iamClient := iam.NewHTTPClient(s.strictMode, s.httpClientTimeout, s.httpClientTLS)
-	metadata, err := s.authorizationServerMetadata(ctx, verifier)
+	metadata, err := iamClient.OAuthAuthorizationServerMetadata(ctx, verifier)
 	if err != nil {
-		return nil, err
+		return nil, fmt.Errorf("failed to retrieve remote OAuth Authorization Server metadata: %w", err)
 	}
 
 	// get the presentation definition from the verifier

auth/services/oauth/relying_party_test.go

@@ -380,27 +380,6 @@ func TestService_CreateJwtBearerToken(t *testing.T) {
 	})
 }
 
-func TestRelyingParty_authorizationServerMetadata(t *testing.T) {
-	t.Run("ok", func(t *testing.T) {
-		ctx := createOAuthRPContext(t)
-
-		metadata, err := ctx.relyingParty.authorizationServerMetadata(context.Background(), ctx.verifierDID)
-
-		require.NoError(t, err)
-		require.NotNil(t, metadata)
-		assert.Equal(t, ctx.authzServerMetadata, *metadata)
-	})
-	t.Run("error - failed to get metadata", func(t *testing.T) {
-		ctx := createOAuthRPContext(t)
-		ctx.metadata = nil
-
-		_, err := ctx.relyingParty.authorizationServerMetadata(context.Background(), ctx.verifierDID)
-
-		require.Error(t, err)
-		assert.EqualError(t, err, "failed to retrieve remote OAuth Authorization Server metadata: server returned HTTP 404 (expected: 200)")
-	})
-}
-
 type rpTestContext struct {
 	ctrl            *gomock.Controller
 	keyStore        *crypto.MockKeyStore