fix: prefetch crash

it was possible that the issuer could be an empty string ('') which would indeed cause the app to crash, since our `invariant` check missed that.
fixes #478

Author: zibs

packages/react-native-app-auth/index.js

@@ -4,29 +4,34 @@ import base64 from 'react-native-base64';
 
 const { RNAppAuth } = NativeModules;
 
+const validateIssuer = issuer => invariant(issuer, 'Config error: issuer must be present');
 const validateIssuerOrServiceConfigurationEndpoints = (issuer, serviceConfiguration) =>
   invariant(
-    typeof issuer === 'string' ||
+    validateIssuer(issuer) ||
+      typeof issuer === 'string' ||
       (serviceConfiguration &&
         typeof serviceConfiguration.authorizationEndpoint === 'string' &&
         typeof serviceConfiguration.tokenEndpoint === 'string'),
     'Config error: you must provide either an issuer or a service endpoints'
   );
 const validateIssuerOrServiceConfigurationRegistrationEndpoint = (issuer, serviceConfiguration) =>
   invariant(
-    typeof issuer === 'string' ||
+    validateIssuer(issuer) ||
+      typeof issuer === 'string' ||
       (serviceConfiguration && typeof serviceConfiguration.registrationEndpoint === 'string'),
     'Config error: you must provide either an issuer or a registration endpoint'
   );
 const validateIssuerOrServiceConfigurationRevocationEndpoint = (issuer, serviceConfiguration) =>
   invariant(
-    typeof issuer === 'string' ||
+    validateIssuer(issuer) ||
+      typeof issuer === 'string' ||
       (serviceConfiguration && typeof serviceConfiguration.revocationEndpoint === 'string'),
     'Config error: you must provide either an issuer or a revocation endpoint'
   );
 const validateIssuerOrServiceConfigurationEndSessionEndpoint = (issuer, serviceConfiguration) =>
   invariant(
-    typeof issuer === 'string' ||
+    validateIssuer(issuer) ||
+      typeof issuer === 'string' ||
       (serviceConfiguration && typeof serviceConfiguration.endSessionEndpoint === 'string'),
     'Config error: you must provide either an issuer or an end session endpoint'
   );