diff --git a/index.html b/index.html
index fcd01b3..1d17a64 100644
--- a/index.html
+++ b/index.html
@@ -15,16 +15,24 @@
             }
         </script>
         <script type="module">
-            import { CachingIssuerProvider, DPoPTokenProvider, ReactiveFetchManager } from "./dist/mod.js"
+            import {
+                CachingAuthorizationServerProvider,
+                CachingIssuerProvider,
+                DPoPTokenProvider,
+                ReactiveFetchManager,
+                XASProvider
+            } from "./dist/mod.js"
             import "./dist/registerElements.js"
 
             /* Reactive fetch infrastructure */
             const ui = document.querySelector("authorization-code-flow")
             const issuerUi = document.querySelector("idp-picker")
             const issuerProvider = new CachingIssuerProvider(issuerUi)
+            const asProvider = new XASProvider(issuerProvider)
+            const cachingASProvider = new CachingAuthorizationServerProvider(asProvider)
             const callbackUri = new URL("/callback.html", location.href).toString()
 
-            const dPoPTokenProvider = new DPoPTokenProvider(callbackUri, ui.getCode.bind(ui), issuerProvider)
+            const dPoPTokenProvider = new DPoPTokenProvider(callbackUri, ui.getCode.bind(ui), cachingASProvider)
 
             const fetch = new ReactiveFetchManager([dPoPTokenProvider]).fetch
 
diff --git a/src/AuthorizationServerProvider.ts b/src/AuthorizationServerProvider.ts
new file mode 100644
index 0000000..587b5a8
--- /dev/null
+++ b/src/AuthorizationServerProvider.ts
@@ -0,0 +1,5 @@
+import * as oauth from "oauth4webapi"
+
+export interface AuthorizationServerProvider {
+    getAuthorizationServer(request: Request): Promise<oauth.AuthorizationServer>
+}
diff --git a/src/CachingAuthorizationServerProvider.ts b/src/CachingAuthorizationServerProvider.ts
new file mode 100644
index 0000000..18f4814
--- /dev/null
+++ b/src/CachingAuthorizationServerProvider.ts
@@ -0,0 +1,15 @@
+import type { AuthorizationServerProvider } from "./AuthorizationServerProvider.js"
+import type * as oauth from "oauth4webapi"
+
+export class CachingAuthorizationServerProvider implements AuthorizationServerProvider {
+    readonly #cache = new Map<string, Promise<oauth.AuthorizationServer>> // TODO: Take cache from caller
+    readonly #original: AuthorizationServerProvider
+
+    constructor(original: AuthorizationServerProvider) {
+        this.#original = original
+    }
+
+    getAuthorizationServer(request: Request): Promise<oauth.AuthorizationServer> {
+        return this.#cache.getOrInsertComputed(request.url, _ => this.#original.getAuthorizationServer(request))
+    }
+}
diff --git a/src/DPoPTokenProvider.ts b/src/DPoPTokenProvider.ts
index 2841703..c05cdb6 100644
--- a/src/DPoPTokenProvider.ts
+++ b/src/DPoPTokenProvider.ts
@@ -2,7 +2,7 @@ import * as oauth from "oauth4webapi"
 import * as DPoP from "dpop"
 import type { GetCodeCallback } from "./GetCodeCallback.js"
 import type { TokenProvider } from "./TokenProvider.js"
-import type { IssuerProvider } from "./IssuerProvider.js"
+import type { AuthorizationServerProvider } from "./AuthorizationServerProvider.js"
 
 type CacheEntry = { created: number, tokenResult: oauth.TokenEndpointResponse, dpopKey: CryptoKeyPair }
 
@@ -10,12 +10,12 @@ export class DPoPTokenProvider implements TokenProvider {
     readonly #getCode: GetCodeCallback
     readonly #callbackUri: string
     readonly #cache = new Map<string, CacheEntry> // TODO: Take cache from caller
-    readonly #issuerProvider: IssuerProvider
+    readonly #asProvider: AuthorizationServerProvider
 
-    constructor(callbackUri: string, getCodeCallback: GetCodeCallback, issuerProvider: IssuerProvider) {
+    constructor(callbackUri: string, getCodeCallback: GetCodeCallback, asProvider: AuthorizationServerProvider) {
         this.#getCode = getCodeCallback
         this.#callbackUri = callbackUri
-        this.#issuerProvider = issuerProvider
+        this.#asProvider = asProvider
     }
 
     async matches(request: Request): Promise<boolean> {
@@ -38,10 +38,7 @@ export class DPoPTokenProvider implements TokenProvider {
         return new Request(request, {headers})
     }
     private async obtainToken(request: Request): Promise<CacheEntry> {
-        const issuer = await this.#issuerProvider.getIssuer(request)
-
-        const discoveryResponse = await oauth.discoveryRequest(issuer, {signal: request.signal})
-        const authorizationServer = await oauth.processDiscoveryResponse(issuer, discoveryResponse)
+        const authorizationServer = await this.#asProvider.getAuthorizationServer(request)
 
         const registrationResponse = await oauth.dynamicClientRegistrationRequest(authorizationServer, {redirect_uris: [this.#callbackUri]}, {signal: request.signal})
         const clientRegistration = await oauth.processDynamicClientRegistrationResponse(registrationResponse)
diff --git a/src/XASProvider.ts b/src/XASProvider.ts
new file mode 100644
index 0000000..feb69dc
--- /dev/null
+++ b/src/XASProvider.ts
@@ -0,0 +1,19 @@
+import type { IssuerProvider } from "./IssuerProvider.js"
+import * as oauth from "oauth4webapi"
+import type { AuthorizationServerProvider } from "./AuthorizationServerProvider.js"
+
+export class XASProvider implements AuthorizationServerProvider {
+    readonly #issuerProvider: IssuerProvider
+
+    constructor(issuerProvider: IssuerProvider) {
+        this.#issuerProvider = issuerProvider
+    }
+
+    async getAuthorizationServer(request: Request): Promise<oauth.AuthorizationServer> {
+        const issuer = await this.#issuerProvider.getIssuer(request)
+        const discoveryResponse = await oauth.discoveryRequest(issuer, {signal: request.signal})
+        const authorizationServer = await oauth.processDiscoveryResponse(issuer, discoveryResponse)
+
+        return authorizationServer
+    }
+}
diff --git a/src/mod.ts b/src/mod.ts
index 2559708..8397108 100644
--- a/src/mod.ts
+++ b/src/mod.ts
@@ -15,3 +15,6 @@ export * from "./WebIdPicker.js"
 export * from "./WebIdRequestCancelledError.js"
 export * from "./IssuerRequestCancelledError.js"
 export * from "./CachingIssuerProvider.js"
+export * from "./AuthorizationServerProvider.js"
+export * from "./XASProvider.js"
+export * from "./CachingAuthorizationServerProvider.js"