nuts-foundation/nuts-node

/*
 * Copyright (C) 2023 Nuts community
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <https://www.gnu.org/licenses/>.
 *
 */

package openid4vci

import (
    "context"
    "encoding/json"
    "errors"
    "fmt"
    "github.com/nuts-foundation/nuts-node/core"
    "net/url"
)

// WalletAPIClient defines a client interface for communicating with a remote wallet over OpenID4VCI.
type WalletAPIClient interface {
    // Metadata returns the OAuth2 client metadata of the remote wallet.
    Metadata() OAuth2ClientMetadata
    // OfferCredential sends a credential offer to the remote wallet.
    OfferCredential(ctx context.Context, offer CredentialOffer) error
}

var _ WalletAPIClient = (*defaultWalletAPIClient)(nil)

// NewWalletAPIClient resolves the OAuth2 credential client metadata from the given URL.
func NewWalletAPIClient(ctx context.Context, httpClient core.HTTPRequestDoer, walletMetadataURL string) (WalletAPIClient, error) {
    if walletMetadataURL == "" {
        return nil, errors.New("empty wallet metadata URL")
    }

    metadata, err := loadOAuth2CredentialsClientMetadata(ctx, walletMetadataURL, httpClient)
    if err != nil {
        return nil, fmt.Errorf("unable to load OAuth2 credential client metadata (url=%s): %w", walletMetadataURL, err)
    }

    return &defaultWalletAPIClient{
        httpClient: httpClient,
        metadata:   *metadata,
    }, nil
}

type defaultWalletAPIClient struct {
    metadata   OAuth2ClientMetadata
    httpClient core.HTTPRequestDoer
}

func (c *defaultWalletAPIClient) Metadata() OAuth2ClientMetadata {
    return c.metadata
}

func (c *defaultWalletAPIClient) OfferCredential(ctx context.Context, offer CredentialOffer) error {
    offerJson, err := json.Marshal(offer)
    if err != nil {
        return err
    }
    requestURL := c.metadata.CredentialOfferEndpoint + "?credential_offer=" + url.QueryEscape(string(offerJson))
    response := CredentialOfferResponse{}
    err = httpGet(ctx, c.httpClient, requestURL, &response)
    if err != nil {
        return fmt.Errorf("offer credential error: %w", err)
    }
    if response.Status != CredentialOfferStatusReceived {
        return fmt.Errorf("offer credential error: unexpected status: %s", response.Status)
    }
    return nil
}

func loadOAuth2CredentialsClientMetadata(ctx context.Context, metadataURL string, httpClient core.HTTPRequestDoer) (*OAuth2ClientMetadata, error) {
    // TODO: what about caching?
    //       See https://github.com/nuts-foundation/nuts-node/issues/2034
    result := OAuth2ClientMetadata{}
    err := httpGet(ctx, httpClient, metadataURL, &result)
    if err != nil {
        return nil, err
    }
    if len(result.CredentialOfferEndpoint) == 0 {
        return nil, errors.New("invalid meta data: does not contain credential offer endpoint")
    }
    return &result, nil
}