diff --git a/src/inMemoryPersister.ts b/src/inMemoryPersister.ts
new file mode 100644
index 0000000..b0a388d
--- /dev/null
+++ b/src/inMemoryPersister.ts
@@ -0,0 +1,13 @@
+import { UserSessionPersister } from './userSessionPersister';
+
+export class InMemoryPersister implements UserSessionPersister {
+  private endOfLife: number = 0;
+  private storage: string = '';
+  public loadUserSession() {
+      return !this.endOfLife || (Date.now() > this.endOfLife) ? '' : this.storage;
+  }
+  public saveUserSession(userSession: string, daysToLive: number) {
+      this.storage = userSession;
+      this.endOfLife = Date.now() + (daysToLive * 24 * 60 * 60 * 1000);
+  }
+}
diff --git a/src/index.ts b/src/index.ts
index 9185589..c520121 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -1,3 +1,4 @@
+import { InMemoryPersister } from './inMemoryPersister';
 import {
     config,
     create,
@@ -12,6 +13,7 @@ import {
 } from './main';
 import { SplitTest } from './splitTest';
 import { uiFactory } from './ui';
+import { CookiePersister, UserSessionPersister } from './userSessionPersister';
 
 const ui = uiFactory(
     testsObservable,
@@ -47,6 +49,9 @@ export {
     reset,
     ui,
     SplitTest,
+    UserSessionPersister,
+    InMemoryPersister,
+    CookiePersister,
 };
 
 export default {
diff --git a/src/main.ts b/src/main.ts
index 773e7ad..aeec0c6 100644
--- a/src/main.ts
+++ b/src/main.ts
@@ -30,6 +30,11 @@ export function config(userConfig: Partial<Config> = {}) {
     if (userConfig.onVariationChange) {
         _config.onVariationChange = userConfig.onVariationChange;
     }
+    if (userConfig.sessionPersister) {
+        const session = _config.sessionPersister.loadUserSession() || '';
+        _config.sessionPersister = userConfig.sessionPersister;
+        _config.sessionPersister.saveUserSession(session, _config.userSessionDaysToLive);
+    }
 }
 
 /**
diff --git a/src/userSessionPersister.ts b/src/userSessionPersister.ts
index 41a18a2..ebc03ff 100644
--- a/src/userSessionPersister.ts
+++ b/src/userSessionPersister.ts
@@ -1,40 +1,35 @@
 import config from './config';
-
 export interface UserSessionPersister {
     loadUserSession(): string | null;
     saveUserSession(userSession: string, daysToLive: number): void;
 }
-
-function createCookie(name: string, value: string, days: number): void {
-    let expires = '';
-    if (days) {
-        const date = new Date();
-        date.setTime(date.getTime() + (days * 24 * 60 * 60 * 1000));
-        expires = '; expires=' + date.toUTCString();
-    }
-    document.cookie = name + '=' + value + expires + '; path=/';
-}
-
-function readCookie(name: string): string | null {
-    const nameEq = name + '=';
-    const ca = document.cookie.split(';');
-    for (let c of ca) {
-        while (c.charAt(0) === ' ') {
-            c = c.substring(1, c.length);
-        }
-        if (c.indexOf(nameEq) === 0) {
-            return c.substring(nameEq.length, c.length);
-        }
-    }
-    return null;
-}
-
 export class CookiePersister implements UserSessionPersister {
-    public loadUserSession() {
-        return readCookie(config.cookieName);
-    }
-
-    public saveUserSession(userSession: string, daysToLive: number) {
-        createCookie(config.cookieName, userSession, daysToLive);
-    }
+  private static createCookie(name: string, value: string, days: number): void {
+      let expires = '';
+      if (days) {
+          const date = new Date();
+          date.setTime(date.getTime() + (days * 24 * 60 * 60 * 1000));
+          expires = '; expires=' + date.toUTCString();
+      }
+      document.cookie = name + '=' + value + expires + '; path=/';
+  }
+  private static readCookie(name: string): string | null {
+      const nameEq = name + '=';
+      const ca = document.cookie.split(';');
+      for (let c of ca) {
+          while (c.charAt(0) === ' ') {
+              c = c.substring(1, c.length);
+          }
+          if (c.indexOf(nameEq) === 0) {
+              return c.substring(nameEq.length, c.length);
+          }
+      }
+      return null;
+  }
+  public loadUserSession() {
+      return CookiePersister.readCookie(config.cookieName);
+  }
+  public saveUserSession(userSession: string, daysToLive: number) {
+    CookiePersister.createCookie(config.cookieName, userSession, daysToLive);
+  }
 }