fix: accept the issuer with or without a trailing slash

Regression introduced with OIDC_ISSUER_MCP. mcpIssuer() stripped the trailing
slash — right for building the JWKS URL, wrong for the `iss` claim check,
which jose compares by exact string. Authentik emits
`.../application/o/shared-memory-mcp/` with the slash, so verification failed
with "claim invalid: iss" even though issuer and audience were both correct.

Before OIDC_ISSUER_MCP the issuer was passed to jwtVerify unstripped and only
stripped when constructing the URL; collapsing both onto the stripped form is
what broke it.

mcpIssuer() now returns the value as configured, the JWKS URL strips locally,
and the claim check accepts both spellings so correctness doesn't hinge on
whether someone typed a trailing slash into an env var.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

apps/web/lib/auth/jwt.ts

@@ -29,7 +29,25 @@ const g = globalThis as GlobalWithJwks;
  * application slug, so this is NOT interchangeable with OIDC_ISSUER.
  */
 export function mcpIssuer(): string {
-  return (env().OIDC_ISSUER_MCP ?? env().OIDC_ISSUER).replace(/\/$/, "");
+  return env().OIDC_ISSUER_MCP ?? env().OIDC_ISSUER;
+}
+
+/**
+ * Issuer values accepted for the `iss` claim.
+ *
+ * jose compares `iss` by exact string, and IdPs are inconsistent about the
+ * trailing slash: Authentik emits `.../application/o/<slug>/` while the same
+ * value is routinely configured without it. Normalizing to one form and
+ * comparing against that fails whenever the two disagree — which is exactly
+ * how this broke: the URL-safe (stripped) form was reused for the claim check
+ * against a token whose `iss` ended in a slash.
+ *
+ * Accept both spellings rather than making correctness depend on how someone
+ * typed an env var.
+ */
+function acceptedIssuers(): [string, string] {
+  const bare = mcpIssuer().replace(/\/$/, "");
+  return [bare, `${bare}/`];
 }
 
 function jwks() {
@@ -37,7 +55,7 @@ function jwks() {
   // Authentik discovery is at `${issuer}/.well-known/openid-configuration`;
   // the JWKS URI is normally `${issuer}/jwks/` or `${issuer}/.well-known/jwks.json`.
   // Authentik canonically serves `${issuer}/jwks/`.
-  const url = new URL(`${mcpIssuer()}/jwks/`);
+  const url = new URL(`${mcpIssuer().replace(/\/$/, "")}/jwks/`);
   g.__sharedMemoryJwks = createRemoteJWKSet(url, {
     cacheMaxAge: 10 * 60 * 1000, // 10 min
     cooldownDuration: 30 * 1000,
@@ -126,7 +144,7 @@ export async function authenticateBearer(authHeader: string | null): Promise<Aut
     }
 
     const { payload } = await jwtVerify(token, jwks(), {
-      issuer: mcpIssuer(),
+      issuer: acceptedIssuers(),
       audience: env().OIDC_AUDIENCE,
     });
     if (!payload.sub) {