Allow adding a path suffix to the OAuth client URI (#7286)

* Allow adding a path suffix to the OAuth client URI

libraries/matrix/api/build.gradle.kts

@@ -24,6 +24,11 @@ android {
     }
 
     defaultConfig {
+        buildConfigField(
+            name = "OAUTH_CLIENT_URI_PATH",
+            type = "String",
+            value = BuildTimeConfig.OAUTH_CLIENT_URL_PATH?.let { "\"$it\"" } ?: "null",
+        )
         buildConfigFieldStr(
             name = "CLIENT_URI",
             value = BuildTimeConfig.URL_WEBSITE ?: "https://element.io"

libraries/matrix/api/src/main/kotlin/io/element/android/libraries/matrix/api/auth/OAuthConfig.kt

@@ -11,7 +11,10 @@ package io.element.android.libraries.matrix.api.auth
 import io.element.android.libraries.matrix.api.BuildConfig
 
 object OAuthConfig {
-    const val CLIENT_URI = BuildConfig.CLIENT_URI
+    val CLIENT_URI = BuildConfig.OAUTH_CLIENT_URI_PATH?.let {
+        // Concatenate the base URI and the path, ensuring there is exactly one '/' between them
+        "${BuildConfig.CLIENT_URI.trimEnd('/')}/${it.trimStart('/')}"
+    } ?: BuildConfig.CLIENT_URI
 
     // Note: host must match with the host of CLIENT_URI
     const val LOGO_URI = BuildConfig.LOGO_URI