diff --git a/src/script/spec/esi_client.spec.ts b/src/script/spec/esi_client.spec.ts
index a24c08b..baa1e34 100644
--- a/src/script/spec/esi_client.spec.ts
+++ b/src/script/spec/esi_client.spec.ts
@@ -61,6 +61,65 @@ describe('EsiClient', () => {
     });
   });
 
+  describe('.parseToken', () => {
+    beforeEach(() => {
+      global.PropertiesService.getScriptProperties = jest.fn().mockReturnValueOnce(
+        createMock<GoogleAppsScript.Properties.Properties>({
+          getProperty(): string {
+            return 'CLIENT_ID';
+          },
+        }),
+      );
+    });
+
+    it('with valid token', () => {
+      global.Utilities.newBlob = jest.fn().mockReturnValueOnce(
+        createMock<GoogleAppsScript.Base.Blob>({
+          getDataAsString(): string {
+            return '{"aud": ["CLIENT_ID", "EVE Online"], "azp": "CLIENT_ID", "iss": "login.eveonline.com"}';
+          },
+        }),
+      );
+
+      expect(ESIClient.parseToken('HEADER.BODY.SIG')).toEqual({
+        aud: ['CLIENT_ID', 'EVE Online'],
+        azp: 'CLIENT_ID',
+        iss: 'login.eveonline.com',
+      });
+      expect(global.Utilities.base64DecodeWebSafe).toHaveBeenCalledWith('BODY');
+    });
+
+    it('with new issuer', () => {
+      global.Utilities.newBlob = jest.fn().mockReturnValueOnce(
+        createMock<GoogleAppsScript.Base.Blob>({
+          getDataAsString(): string {
+            return '{"aud": ["CLIENT_ID", "EVE Online"], "azp": "CLIENT_ID", "iss": "https://login.eveonline.com"}';
+          },
+        }),
+      );
+
+      expect(ESIClient.parseToken('HEADER.BODY.SIG')).toEqual({
+        aud: ['CLIENT_ID', 'EVE Online'],
+        azp: 'CLIENT_ID',
+        iss: 'https://login.eveonline.com',
+      });
+      expect(global.Utilities.base64DecodeWebSafe).toHaveBeenCalledWith('BODY');
+    });
+
+    it('with invalid issuer', () => {
+      global.Utilities.newBlob = jest.fn().mockReturnValueOnce(
+        createMock<GoogleAppsScript.Base.Blob>({
+          getDataAsString(): string {
+            return '{"aud": ["CLIENT_ID", "EVE Online"], "azp": "CLIENT_ID", "iss": "login.eveonline.net"}';
+          },
+        }),
+      );
+
+      expect(() => ESIClient.parseToken('HEADER.BODY.SIG')).toThrow('Access token validation error: invalid issuer');
+      expect(global.Utilities.base64DecodeWebSafe).toHaveBeenCalledWith('BODY');
+    });
+  });
+
   describe('#setFunction', () => {
     beforeEach(() => {
       endpointProvider.hasEndpoint = jest.fn().mockReturnValueOnce(false);
diff --git a/src/script/spec/index.ts b/src/script/spec/index.ts
index 388dd68..4567764 100644
--- a/src/script/spec/index.ts
+++ b/src/script/spec/index.ts
@@ -1 +1,6 @@
 import 'jest-ts-auto-mock';
+import { createMock } from 'ts-auto-mock';
+
+// Mock AppScript types
+global.Utilities = createMock<GoogleAppsScript.Utilities.Utilities>();
+global.PropertiesService = createMock<GoogleAppsScript.Properties.PropertiesService>();
diff --git a/src/script/src/esi_client.ts b/src/script/src/esi_client.ts
index 35caff1..aaa8993 100644
--- a/src/script/src/esi_client.ts
+++ b/src/script/src/esi_client.ts
@@ -17,8 +17,10 @@ interface IHTTPClient {
 class ESIClient {
   private static readonly BASE_URL = 'https://esi.evetech.net';
   private static readonly AUDIENCE = 'EVE Online';
-  private static readonly ISSUER = 'login.eveonline.com';
-  private static readonly ISSUER_URL_SCHEMA = 'https://login.eveonline.com';
+  private static readonly ISSUERS = [
+    'login.eveonline.com',
+    'https://login.eveonline.com'
+  ];
 
   public static addQueryParam(path: string, paramName: string, paramValue: any): string {
     path += path.includes('?') ? '&' : '?';
@@ -30,7 +32,7 @@ class ESIClient {
     const jwtToken: IAccessTokenData = JSON.parse(Utilities.newBlob(Utilities.base64DecodeWebSafe(access_token.split('.')[1])).getDataAsString());
     const clientId: string = getScriptProperties_().getProperty('CLIENT_ID')!;
 
-    if (jwtToken.iss !== ESIClient.ISSUER && jwtToken.iss !== ESIClient.ISSUER_URL_SCHEMA) throw 'Access token validation error: invalid issuer';
+    if (!ESIClient.ISSUERS.includes(jwtToken.iss)) throw 'Access token validation error: invalid issuer';
     if (jwtToken.aud[0] !== clientId || jwtToken.aud[1] !== ESIClient.AUDIENCE) throw 'Access token validation error: invalid audience';
     if (jwtToken.azp !== clientId) throw 'Access token validation error: invalid authorized party';
     return jwtToken;