diff --git a/src/Cache.ts b/src/Cache.ts
new file mode 100644
index 0000000..f94a0a9
--- /dev/null
+++ b/src/Cache.ts
@@ -0,0 +1,5 @@
+export interface Cache<T extends NonNullable<unknown>> {
+    getItem(key: string): Promise<T | null>
+    setItem(key: string, value: T): Promise<void>
+    removeItem(key: string): Promise<void>
+}
diff --git a/src/CachingAuthorizationServerProvider.ts b/src/CachingAuthorizationServerProvider.ts
index 267db11..abc1931 100644
--- a/src/CachingAuthorizationServerProvider.ts
+++ b/src/CachingAuthorizationServerProvider.ts
@@ -1,8 +1,10 @@
+import type { Cache } from "./Cache.js"
+import { MemoryCache } from "./MemoryCache.js"
 import type { AuthorizationServerProvider } from "./AuthorizationServerProvider.js"
 import type * as oauth from "oauth4webapi"
 
 export class CachingAuthorizationServerProvider implements AuthorizationServerProvider {
-    readonly #cache = new Map<string, oauth.AuthorizationServer> // TODO: Take cache from caller
+    readonly #cache: Cache<oauth.AuthorizationServer> = new MemoryCache // TODO: Take cache from caller
     readonly #original: AuthorizationServerProvider
 
     constructor(original: AuthorizationServerProvider) {
@@ -10,13 +12,13 @@ export class CachingAuthorizationServerProvider implements AuthorizationServerPr
     }
 
     async getAuthorizationServer(request: Request): Promise<oauth.AuthorizationServer> {
-        const cached = this.#cache.get(request.url)
-        if (cached !== undefined) {
+        const cached = await this.#cache.getItem(request.url)
+        if (cached !== null) {
             return cached
         }
 
         const fresh = await this.#original.getAuthorizationServer(request)
-        this.#cache.set(request.url, fresh)
+        await this.#cache.setItem(request.url, fresh)
         return fresh
     }
 }
diff --git a/src/CachingClientProvider.ts b/src/CachingClientProvider.ts
index ddda929..fbd0f09 100644
--- a/src/CachingClientProvider.ts
+++ b/src/CachingClientProvider.ts
@@ -1,8 +1,10 @@
+import type { Cache } from "./Cache.js"
+import { MemoryCache } from "./MemoryCache.js"
 import type { ClientProvider } from "./ClientProvider.js"
 import type * as oauth from "oauth4webapi"
 
 export class CachingClientProvider implements ClientProvider {
-    readonly #cache = new Map<string, oauth.Client> // TODO: Take cache from caller
+    readonly #cache: Cache<oauth.Client> = new MemoryCache // TODO: Take cache from caller
     readonly #original: ClientProvider
 
     constructor(original: ClientProvider) {
@@ -10,13 +12,13 @@ export class CachingClientProvider implements ClientProvider {
     }
 
     async getClient(as: oauth.AuthorizationServer, redirectUri: string, signal: AbortSignal): Promise<oauth.Client> {
-        const cached = this.#cache.get(as.issuer)
-        if (cached !== undefined) {
+        const cached = await this.#cache.getItem(as.issuer)
+        if (cached !== null) {
             return cached
         }
 
         const fresh = await this.#original.getClient(as, redirectUri, signal)
-        this.#cache.set(as.issuer, fresh)
+        await this.#cache.setItem(as.issuer, fresh)
         return fresh
     }
 }
diff --git a/src/CachingIssuerProvider.ts b/src/CachingIssuerProvider.ts
index 992342f..64efb4d 100644
--- a/src/CachingIssuerProvider.ts
+++ b/src/CachingIssuerProvider.ts
@@ -1,7 +1,9 @@
+import type { Cache } from "./Cache.js"
+import { MemoryCache } from "./MemoryCache.js"
 import { IssuerProvider } from "./IssuerProvider.js"
 
 export class CachingIssuerProvider implements IssuerProvider {
-    readonly #cache = new Map<string, URL> // TODO: Take cache from caller
+    readonly #cache: Cache<URL> = new MemoryCache // TODO: Take cache from caller
     readonly #original: IssuerProvider
 
     constructor(original: IssuerProvider) {
@@ -9,13 +11,13 @@ export class CachingIssuerProvider implements IssuerProvider {
     }
 
     async getIssuer(request: Request): Promise<URL> {
-        const cached = this.#cache.get(request.url)
-        if (cached !== undefined) {
+        const cached = await this.#cache.getItem(request.url)
+        if (cached !== null) {
             return cached
         }
 
         const fresh = await this.#original.getIssuer(request)
-        this.#cache.set(request.url, fresh)
+        await this.#cache.setItem(request.url, fresh)
         return fresh
     }
 }
diff --git a/src/DPoPTokenProvider.ts b/src/DPoPTokenProvider.ts
index d577955..574f552 100644
--- a/src/DPoPTokenProvider.ts
+++ b/src/DPoPTokenProvider.ts
@@ -5,6 +5,8 @@ import type { TokenProvider } from "./TokenProvider.js"
 import type { AuthorizationServerProvider } from "./AuthorizationServerProvider.js"
 import { ClientProvider } from "./ClientProvider.js"
 import { supportsOfflineAccess } from "./supportsOfflineAccess.js"
+import type { Cache } from "./Cache.js"
+import { MemoryCache } from "./MemoryCache.js"
 
 type CacheEntry = {
     created: number,
@@ -20,7 +22,7 @@ export class DPoPTokenProvider implements TokenProvider {
 
     // TODO: Take cache from caller
     // TODO: Once cache is externalized, document that it should not be shared between clients (which would lead to impersonation)
-    readonly #cache = new Map<string, CacheEntry>
+    readonly #cache: Cache<CacheEntry> = new MemoryCache
     readonly #asProvider: AuthorizationServerProvider
     readonly #clientProvider: ClientProvider
 
@@ -52,23 +54,23 @@ export class DPoPTokenProvider implements TokenProvider {
 
     private async getCachedToken(request: Request): Promise<CacheEntry> {
         // TODO: More robust key via callback to support complex caching scenarios
-        const cached = this.#cache.get(request.url)
+        const cached = await this.#cache.getItem(request.url)
 
         // TODO: Support actively refreshing the token
-        if (cached !== undefined) {
+        if (cached !== null) {
             if (!isExpired(cached)) {
                 return cached
             }
 
             const refreshed = await this.refreshToken(cached, request)
             if (refreshed !== undefined) {
-                this.#cache.set(request.url, refreshed)
+                await this.#cache.setItem(request.url, refreshed)
                 return refreshed
             }
         }
 
         const fresh = await this.obtainToken(request)
-        this.#cache.set(request.url, fresh)
+        await this.#cache.setItem(request.url, fresh)
 
         return fresh
     }
@@ -155,7 +157,7 @@ export class DPoPTokenProvider implements TokenProvider {
             const tokenResponse = await oauth.refreshTokenGrantRequest(cached.authorizationServer, cached.client, this.getClientAuth(cached.authorizationServer.issuer, cached.client), cached.tokenResult.refresh_token, options)
             tokenResult = await oauth.processRefreshTokenResponse(cached.authorizationServer, cached.client, tokenResponse)
         } catch (e) {
-            this.#cache.delete(request.url)
+            await this.#cache.removeItem(request.url)
 
             if (e instanceof oauth.ResponseBodyError && e.error === "invalid_grant") {
                 console.debug("Access token could not be refreshed")
diff --git a/src/MemoryCache.ts b/src/MemoryCache.ts
new file mode 100644
index 0000000..4c5203b
--- /dev/null
+++ b/src/MemoryCache.ts
@@ -0,0 +1,17 @@
+import type { Cache } from "./Cache.js"
+
+export class MemoryCache<T extends NonNullable<unknown>> implements Cache<T> {
+    readonly #values = new Map<string, T>
+
+    async getItem(key: string): Promise<T | null> {
+        return this.#values.get(key) ?? null
+    }
+
+    async setItem(key: string, value: T): Promise<void> {
+        this.#values.set(key, value)
+    }
+
+    async removeItem(key: string): Promise<void> {
+        this.#values.delete(key)
+    }
+}