diff --git a/src/authentication/Credentials.ts b/src/authentication/Credentials.ts
index 284067871..826af0cda 100644
--- a/src/authentication/Credentials.ts
+++ b/src/authentication/Credentials.ts
@@ -5,4 +5,5 @@ export type Credentials = {
   agent?: { webId: string };
   client?: { clientId: string };
   issuer?: { url: string };
+  [key: string]: unknown;
 };
diff --git a/src/authorization/Authorizer.ts b/src/authorization/Authorizer.ts
index 161f249f4..4c32df1c4 100644
--- a/src/authorization/Authorizer.ts
+++ b/src/authorization/Authorizer.ts
@@ -18,7 +18,7 @@ export interface AuthorizerInput {
 }
 
 /**
- * Verifies if the credentials provide access with the given permissions on the resource.
- * An {@link Error} with the necessary explanation will be thrown when permissions are not granted.
+ * Verifies whether the credentials provide access with the given permissions on the resource.
+ * An {@link Error} with the necessary explanation will be thrown if permissions are not granted.
  */
 export abstract class Authorizer extends AsyncHandler<AuthorizerInput> {}
diff --git a/src/authorization/PermissionBasedAuthorizer.ts b/src/authorization/PermissionBasedAuthorizer.ts
index 1294df5d4..a48c9d305 100644
--- a/src/authorization/PermissionBasedAuthorizer.ts
+++ b/src/authorization/PermissionBasedAuthorizer.ts
@@ -13,7 +13,7 @@ import { AccessMode } from './permissions/Permissions';
 /**
  * Authorizer that bases its decision on the output it gets from its PermissionReader.
  * For each permission it checks if the reader allows that for at least one credential type,
- * if yes authorization is granted.
+ * if yes, authorization is granted.
  * `undefined` values for reader results are interpreted as `false`.
  */
 export class PermissionBasedAuthorizer extends Authorizer {
@@ -37,7 +37,9 @@ export class PermissionBasedAuthorizer extends Authorizer {
     // Ensure all required modes are within the agent's permissions.
     for (const [ identifier, modes ] of requestedModes.entrySets()) {
       const modeString = [ ...modes ].join(',');
-      this.logger.debug(`Checking if ${credentials.agent?.webId} has ${modeString} permissions for ${identifier.path}`);
+      this.logger.debug(
+        `Checking if ${JSON.stringify(credentials)} has ${modeString} permissions for ${identifier.path}`,
+      );
       const permissionSet = availablePermissions.get(identifier) ?? {};
       for (const mode of modes) {
         try {
@@ -82,7 +84,7 @@ export class PermissionBasedAuthorizer extends Authorizer {
   private requireModePermission(credentials: Credentials, permissionSet: PermissionSet, mode: AccessMode): void {
     if (!permissionSet[mode]) {
       if (this.isAuthenticated(credentials)) {
-        this.logger.warn(`Agent ${credentials.agent!.webId} has no ${mode} permissions`);
+        this.logger.warn(`Agent ${JSON.stringify(credentials)} has no ${mode} permissions`);
         throw new ForbiddenHttpError();
       } else {
         // Solid, §2.1: "When a client does not provide valid credentials when requesting a resource that requires it,
@@ -99,6 +101,6 @@ export class PermissionBasedAuthorizer extends Authorizer {
    * @param credentials - Credentials to check.
    */
   private isAuthenticated(credentials: Credentials): boolean {
-    return typeof credentials.agent?.webId === 'string';
+    return Object.values(credentials).some((cred): boolean => cred !== undefined);
   }
 }
diff --git a/src/authorization/PermissionReader.ts b/src/authorization/PermissionReader.ts
index cccb3ace3..552a211de 100644
--- a/src/authorization/PermissionReader.ts
+++ b/src/authorization/PermissionReader.ts
@@ -16,7 +16,7 @@ export interface PermissionReaderInput {
 
 /**
  * Discovers the permissions of the given credentials on the given identifier.
- * In case the reader finds no permission for the requested identifiers and credentials
+ * If the reader finds no permission for the requested identifiers and credentials,
  * it can return an empty or incomplete map.
  */
 export abstract class PermissionReader extends AsyncHandler<PermissionReaderInput, PermissionMap> {}