diff --git a/lib/index.js b/lib/index.js
index 35ada40..85f31ca 100644
--- a/lib/index.js
+++ b/lib/index.js
@@ -49,6 +49,7 @@ export async function signCapabilityInvocation({
   capabilityAction,
   invocationSigner,
   created = Math.floor(Date.now() / 1000),
+  authzHeaderName = 'authorization',
   expires
 }) {
   try {
@@ -75,6 +76,9 @@ export async function signCapabilityInvocation({
         '"capability" must be a string to invoke a root capability or an ' +
         'object to invoke a delegated capability.');
     }
+    if(!(authzHeaderName && typeof authzHeaderName === 'string')) {
+      throw new TypeError('"authzHeaderName" must be a string.');
+    }
 
     // if capability is a root zcap, use just its ID
     if(typeof capability === 'object' && !capability.parentCapability) {
@@ -135,7 +139,7 @@ export async function signCapabilityInvocation({
     const data = new TextEncoder().encode(plaintext);
     const signature = base64Encode(await invocationSigner.sign({data}));
 
-    signed.authorization = createAuthzHeader({
+    signed[authzHeaderName.toLowerCase()] = createAuthzHeader({
       includeHeaders,
       keyId,
       signature,