Address old @adam-vessey comment.

Author: ruebot

src/IIIFManifestParser.php

@@ -87,11 +87,16 @@ public function getTileSources($manifest_url, $access_token = NULL) {
 
     try {
       // Request the manifest.
-      $manifest_response = $this->httpClient->request('GET', $manifest_url, [
-        'headers' => [
-          'Authorization' => 'Bearer ' . $access_token,
-        ],
-      ]);
+      if (empty($access_token)) {
+        $manifest_response = $this->httpClient->get($manifest_url);
+      }
+      else {
+        $manifest_response = $this->httpClient->request('GET', $manifest_url, [
+          'headers' => [
+            'Authorization' => 'Bearer ' . $access_token,
+          ],
+        ]);
+      }
 
       // Decode the manifest json.
       $manifest_string = (string) $manifest_response->getBody();

tests/src/Kernel/IIIFManifestParserTest.php

@@ -210,9 +210,7 @@ public function testGetTileSourcesWithTokens() {
       $logger
     );
 
-    $access_token = 'islandora';
-
-    $tile_sources = $parser->getTileSources('http://example.org/node/[node:nid]/manifest', $access_token);
+    $tile_sources = $parser->getTileSources('http://example.org/node/[node:nid]/manifest');
     $expected = [
       'http://127.0.0.1:8080/cantaloupe/iiif/2/derp.TIF',
       'http://127.0.0.1:8080/cantaloupe/iiif/2/derp.jpeg',