Probe editor capability endpoints instead of trusting the route list

WordPress/src/main/java/org/wordpress/android/repositories/EditorAuthHeaderBuilder.kt

@@ -0,0 +1,90 @@
+package org.wordpress.android.repositories
+
+import android.util.Base64
+import org.wordpress.android.fluxc.model.SiteModel
+import org.wordpress.android.util.AppLog
+import javax.inject.Inject
+import javax.inject.Singleton
+
+/**
+ * Builds the `Authorization` header that the editor — and editor
+ * capability probes — use when talking to a site. Centralised so the
+ * probe in [EditorSettingsRepository] cannot drift from what
+ * [org.wordpress.android.ui.posts.GutenbergKitSettingsBuilder] hands
+ * to GutenbergKit at launch.
+ *
+ * - WP.com-routed sites (JPC, Atomic, WPCom) → `Bearer <token>`
+ * - Self-hosted sites with an application password → `Basic <base64>`
+ *
+ * Returns `null` when the required credentials are missing.
+ */
+@Singleton
+class EditorAuthHeaderBuilder @Inject constructor() {
+    /**
+     * Convenience overload that derives [shouldUseWPComRestApi] and
+     * credentials from [site].
+     */
+    fun build(site: SiteModel, accessToken: String?): String? {
+        val applicationPassword = site.apiRestPasswordPlain
+        val shouldUseWPComRestApi =
+            applicationPassword.isNullOrEmpty() && site.isUsingWpComRestApi
+        return build(
+            shouldUseWPComRestApi = shouldUseWPComRestApi,
+            accessToken = accessToken,
+            username = site.apiRestUsernamePlain,
+            password = applicationPassword,
+        )
+    }
+
+    fun build(
+        shouldUseWPComRestApi: Boolean,
+        accessToken: String?,
+        username: String?,
+        password: String?,
+    ): String? = if (shouldUseWPComRestApi) {
+        buildBearer(accessToken)
+    } else {
+        buildBasic(username, password)
+    }
+
+    private fun buildBearer(accessToken: String?): String? =
+        if (!accessToken.isNullOrEmpty()) {
+            "$AUTH_BEARER_PREFIX$accessToken"
+        } else {
+            AppLog.w(
+                AppLog.T.EDITOR,
+                "Missing access token for WP.com REST API authentication"
+            )
+            null
+        }
+
+    private fun buildBasic(username: String?, password: String?): String? {
+        if (username.isNullOrEmpty() || password.isNullOrEmpty()) {
+            AppLog.w(
+                AppLog.T.EDITOR,
+                "Incomplete credentials for Basic authentication"
+            )
+            return null
+        }
+        return try {
+            val credentials = "$username:$password"
+            val encoded = Base64.encodeToString(
+                credentials.toByteArray(Charsets.UTF_8),
+                Base64.NO_WRAP
+            )
+            "$AUTH_BASIC_PREFIX$encoded"
+        } catch (e: IllegalArgumentException) {
+            AppLog.e(
+                AppLog.T.EDITOR,
+                "Failed to encode Basic auth credentials",
+                e
+            )
+            null
+        }
+    }
+
+    companion object {
+        private const val AUTH_BEARER_PREFIX = "Bearer "
+        private const val AUTH_BASIC_PREFIX = "Basic "
+    }
+}