# Imagehoster

Imagehoster is [opensource community software](https://gitlab.syncad.com/hive/imagehoster) that helps you to proxy user uploaded images and allows you to create easy user authenticated image uploads with extra benefits (rate limiting based on reputation, blacklist, etc.)

There are couple instance of imagehosters run by different teams, [https://images.hive.blog](https://images.hive.blog/) and [https://images.ecency.com](https://images.ecency.com/) separately maintained/hosted instance of Imagehoster. You can also start your own instance easily by following [Readme](https://gitlab.syncad.com/hive/imagehoster#imagehoster) and [Devportal](https://developers.hive.io/services/#services-imagehoster) guides.

If user login to your app with Hivesigner, you can verify user and accept their uploads by utilizing techniques used by Imagehoster, above instances does that and verify `access_token` for uploads.

`POST /hs/:accesstoken`

Above endpoint takes `access_token` and verifies if it was created by same app, in above instances, `@hive.blog` and `@ecency.app`, when you setting up your own instance of imagehoster, your users in your app will be able to verify and upload images to your instance. Below is code section to show how verification is done.

```
    // take access token from url params
    const token = ctx.params['accesstoken']
    //decode access token
    const decoded = Buffer.from(b64uToB64(token), 'base64').toString()
    // parse it into object
    const tokenObj = JSON.parse(decoded)
    const signedMessage = tokenObj.signed_message
    if (
        tokenObj.authors
        && tokenObj.authors[0]
        && tokenObj.signatures
        && tokenObj.signatures[0]
        && signedMessage
        && signedMessage.type
        && ['login', 'posting', 'offline', 'code', 'refresh']
        .includes(signedMessage.type)
        && signedMessage.app
    ) {
        // get username from access_token
        const username = tokenObj.authors[0]

        let account = {
            name: '',
            reputation: 0,
        }
        // initialize Hivesigner with user access_token and app_account from imagehoster config
        const cl = new hivesigner.Client({
            app: UPLOAD_LIMITS.app_account,
            accessToken: token,
        })

        await cl.me(function (err: any, res: any) {
            if (!err && res) {
                account = res.account
                APIError.assert(account, APIError.Code.NoSuchAccount)

                ctx.log.warn('uploading app %s', signedMessage.app)
                APIError.assert(username === account.name, APIError.Code.InvalidSignature)
                // user access_token should have same signed app account as imagehoster defined app account.
                APIError.assert(signedMessage.app === UPLOAD_LIMITS.app_account, APIError.Code.InvalidSignature)
                APIError.assert(res.scope.includes('comment'), APIError.Code.InvalidSignature)
                // check if user has authorized posting authority to app_account
                if (account && account.name) {
                    ['posting', 'active', 'owner'].forEach((type) => {
                      account[type].account_auths.forEach((key: string[]) => {
                        if (
                          !validSignature
                          && key[0] === UPLOAD_LIMITS.app_account
                        ) {
                          validSignature = true;
                        }
                      });
                    });
                }
            }
        });
      }
```

This is simple verification method use only app accounts to verify `access_token` and validity of user.


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