You should use this option if you wish to protect app secrets, including API keys. Rather than build secrets into an app, where they might be reverse engineered, they are only provided at runtime by Approov for apps that pass attestation. This substantially improves your protection and prevents these secrets being abused by attackers.
These additional steps require access to the Approov CLI, please follow the Installation instructions.
In order for secrets or API keys to be protected when being transmitted externally by the app, it is necessary to inform Approov about the domains on which they may be sent. Execute the following command:
approov api -add your.domain -noApproovToken
This informs Approov that it should be active for the domain, but does not need to send Approov tokens for it. Adding the domain uses Managed Trust Roots to ensure that the channel will be protected against Man-in-the-Middle (MitM) attacks.
It is assumed that you already have some client secrets and/or API keys in your app that you would like to migrate for protection by Approov. You must inform Approov what the value of each secret is as follows:
approov secstrings -addKey your-secret-name -predefinedValue your-secret-value
Note that this command requires an admin role.
These values can be changed at any time and will propagate within 5 minutes to all running instances of your apps. Since earlier released versions of the app may have already leaked your-secret-value, you may wish to refresh the secret at some later point when any older version of the app is no longer in use. You can of course do this update over-the-air using Approov without any need to modify the app.
You can define up to 16 different secret values in this way.
If the secret is presented in an API header or query parameter, and you are able to use the ApproovService networking stack, then Approov can automatically substitute the secret value at runtime. You should use this method wherever possible.
If the published code of your app currently uses your-secret-value then replace it with the value your-secret-name. This provides a placeholder value which can then be automatically substituted with the actual secret value at runtime, for validly attesting apps. The shipped app code will only contain the placeholder values.
If the secret value needs to be provided on the header your-header then it is necessary to notify the ApproovService that the header is subject to substitution. You do this by making the call once:
ApproovService.addSubstitutionHeader("your-header", null);With this in place the Approov networking interceptor should replace the your-secret-name with your-secret-value as required when the app passes attestation. Since the mapping lookup is performed on the secret name you have the flexibility of providing different secrets on different API calls, even if they are passed with the same header name.
You can see a worked example for the Shapes app.
If the secret value is provided as a parameter in a URL query string then it is necessary to call a function that may rewrite the URL. This must be done before the request is made. For instance, if you wish to substitute the parameter your-param then you must call:
uri = await ApproovService.substituteQueryParam(uri, "your-param");If no substitution is made then the return value is the same as the input Uri, otherwise a new Uri is created with the substituted parameter value. The call should transform any instance of a URL such as https://your.domain/endpoint?your-param=your-secret-name into https://your.domain/endpoint?your-param=your-secret-value. The function call may throw ApproovException which you must handle. Note that this should only ever be applied to a Uri with a host domain that has been added to Approov, so that either pinning or managed trust roots protection is being applied.
In some cases it might not be possible to automatically substitute a secret in a header or query parameter. This might be because the secret is used in other ways in your application.
In this case it is possible to make an explicit call at runtime to obtain the secret value, for apps passing attestation. Here is an example for using the required method in ApproovService:
String? secret;
try {
secret = await ApproovService.fetchSecureString("your-secret-name", null);
}
on ApproovRejectionException catch(e) {
// failure due to the attestation being rejected, e.arc and e.rejectionReasons may be used
}
on ApproovNetworkException catch(e) {
// failure due to a potentially temporary networking issue, allow for a user initiated retry
}
on ApproovException catch(e) {
// a more permanent error, see e.cause
}
// use `secret` as required, but never cache or store its value - note `secret` will be null
// if it is not definedIMPORTANT: The secrets obtained should only ever be communicated externally from the app over channels using the Approov networking stack and which have been added as protected API domains. If not then it is possible for them to be intercepted by a Man-in-the-Middle (MitM) attack.
If the app is not recognized as being valid by Approov then an ApproovRejectionException is thrown on the request and the API call is not completed. The secret value will never be communicated to the app in this case.
Your app should specifically catch this exception and provide some feedback to the user to explain why the app is not working. The ApproovRejectionException has a arc member which provides an Attestation Response Code which can provide more information about the status of the device, without revealing any details to the end user.
If you wish to provide more direct feedback then enable the Rejection Reasons feature:
approov policy -setRejectionReasons on
Note that this command requires an admin role.
You will then be able to use the rejectionReasons member on an ApproovRejectionException to obtain a comma separated list of device properties responsible for causing the rejection.
You should add the signing certificate used to sign apps so that Approov can recognize your app as being official.
Add the local certificate used to sign apps in Android Studio. The following assumes it is in PKCS12 format:
approov appsigncert -add ~/.android/debug.keystore -storePassword android -autoReg
See Android App Signing Certificates if your keystore format is not recognized or if you have any issues adding the certificate. This also provides information about adding certificates for when releasing to the Play Store. Note also that you need to apply specific Android Obfuscation rules when creating an app release.
These are available in your Apple development account portal. Go to the initial screen showing program resources:
Click on Certificates and you will be presented with the full list of development and distribution certificates for the account. Click on the certificate being used to sign applications from your particular Xcode installation and you will be presented with the following dialog:
Now click on the Download button and a file with a .cer extension is downloaded, e.g. development.cer. Add it to Approov with:
approov appsigncert -add development.cer -autoReg
If it is not possible to download the correct certificate from the portal then it is also possible to add app signing certificates from the app.
IMPORTANT: Apps built to run on the iOS simulator are not code signed and thus auto-registration does not work for them. In this case you can consider forcing a device ID to pass to get a valid attestation.
See Exploring Other Approov Features for information about additional Approov features you may wish to try.
You may wish to set a development key in order to force an app to be passed, if it may be resigned by a different app signing certificate to which you don't have access. Perform the call:
ApproovService.setDevKey("uDW9FuLVpL1_4zo1")See using a development key to understand how to obtain the development key which is the parameter to the call.
In some cases the value to be substituted on a header may be prefixed by some fixed string. A common case is the presence of Bearer included in an authorization header to indicate the use of a bearer token. In this case you can specify a prefix as follows:
ApproovService.addSubstitutionHeader("Authorization", "Bearer ");This causes the Bearer prefix to be stripped before doing the lookup for the substitution, and the Bearer prefix added to the actual secret value as part of the substitution.
In addition to secret values defined in the Approov cloud, it is also possible to get and set secure string values independently for each app instance. These are never communicated to the Approov cloud service, but are encrypted at rest using keys which can only be retrieved by passing apps. You can use this feature to protect user authorization tokens issued to individual apps or other sensitive customer data, for instance.
App instance secure strings can be set and retrived using the secret fetching code. You can define a new value for a given secret name by passing a value in the second parameter of fetchSecureString, rather than null. An empty string may be used to delete the secure string completely.
If you wish to reduce the latency associated with substituting the first secret, then construct an ApproovClient soon after app initialization (to provide the configuration string) and then call:
ApproovService.prefetch()This initiates the process of fetching the required information as a background task, so that it is available immediately when subsequently needed. Note the information will automatically expire after approximately 5 minutes.
You may wish to do an early check in your app to present a warning to the user if it is not going to be able to access secrets because it fails the attestation process. Here is an example of calling the appropriate method in ApproovService:
try {
await ApproovService.precheck();
}
on ApproovRejectionException catch(e) {
// failure due to the attestation being rejected, e.arc and e.rejectionReasons may be used to
// present information to the user (note e.rejectionReasons is only available if the feature is
// enabled, otherwise it is always an empty string)
}
on ApproovNetworkException catch(e) {
// failure due to a potentially temporary networking issue, allow for a user initiated retry
}
on ApproovException catch(e) {
// a more permanent error, see e.cause
}
// app has passed the precheckNote you should NEVER use this as the only form of protection in your app, this is simply to provide an early indication of failure to your users as a convenience. You must always also have secrets essential to the operation of your app, or access to backend API services, protected with Approov. This is because, although the Approov attestation itself is heavily secured, it may be possible for an attacker to bypass its result or prevent it being called at all. When the app is dependent on the secrets protected, it is not possible for them to be obtained at all without passing the attestation.