Make sure the key store alias is globally unique

If a user has installed multiple apps with this SDK, Android will throw
an exception when the second app tries to use the same key pair alias.
This will crash our SDK and the App. This commit makes sure the key is
unique by including the property id in the string.

Author: 0x7f

lib/src/main/java/de/contentpass/lib/ContentPass.kt

@@ -112,7 +112,7 @@ class ContentPass internal constructor(
         fun build(): ContentPass {
             configuration = grabConfiguration()
             val authorizer = Authorizer(configuration!!, context!!)
-            val store = TokenStore(context!!, KeyStore(context!!))
+            val store = TokenStore(context!!, KeyStore(context!!, configuration!!.propertyId))
             return ContentPass(authorizer, store, configuration!!)
         }
 

lib/src/main/java/de/contentpass/lib/KeyStore.kt

@@ -18,9 +18,9 @@ import javax.crypto.spec.SecretKeySpec
 import javax.security.auth.x500.X500Principal
 import java.security.KeyStore as VendorKeyStore
 
-internal class KeyStore(private val context: Context) {
+internal class KeyStore(private val context: Context, private val propertyId: String) {
     private val keystoreName = "AndroidKeyStore"
-    private val keyPairAlias = "de.contentpass.KeyPair"
+    private val keyPairAlias = "de.contentpass.KeyPair.$propertyId"
     private val privateKey: PrivateKey
     private val publicKey: PublicKey
     private val keystore = VendorKeyStore.getInstance(keystoreName)

lib/src/test/java/de/contentpass/lib/KeyStoreTests.kt

@@ -0,0 +1,51 @@
+package de.contentpass.lib
+
+import android.content.Context
+import io.mockk.mockk
+import org.junit.Assert.assertEquals
+import org.junit.Test
+import java.lang.reflect.Field
+
+class KeyStoreTests {
+
+    @Test
+    fun `key pair alias contains property id`() {
+        val propertyId = "test-property-123"
+        val context: Context = mockk(relaxed = true)
+
+        // Use reflection to access the private keyPairAlias field
+        val keyStore = KeyStore(context, propertyId)
+        val keyPairAliasField: Field = KeyStore::class.java.getDeclaredField("keyPairAlias")
+        keyPairAliasField.isAccessible = true
+        val keyPairAlias: String = keyPairAliasField.get(keyStore) as String
+
+        // Verify the alias contains the property ID
+        assertEquals("de.contentpass.KeyPair.$propertyId", keyPairAlias)
+        assertEquals(true, keyPairAlias.contains(propertyId))
+    }
+
+    @Test
+    fun `key pair alias uses different property ids correctly`() {
+        val propertyId1 = "property-one"
+        val propertyId2 = "property-two"
+        val context: Context = mockk(relaxed = true)
+
+        // Create two KeyStore instances with different property IDs
+        val keyStore1 = KeyStore(context, propertyId1)
+        val keyStore2 = KeyStore(context, propertyId2)
+
+        val keyPairAliasField: Field = KeyStore::class.java.getDeclaredField("keyPairAlias")
+        keyPairAliasField.isAccessible = true
+
+        val alias1: String = keyPairAliasField.get(keyStore1) as String
+        val alias2: String = keyPairAliasField.get(keyStore2) as String
+
+        // Verify each alias contains its respective property ID
+        assertEquals("de.contentpass.KeyPair.$propertyId1", alias1)
+        assertEquals("de.contentpass.KeyPair.$propertyId2", alias2)
+        
+        // Verify they are different
+        assertEquals(false, alias1 == alias2)
+    }
+}
+