src/lib/sha256.test.ts

@@ -0,0 +1,44 @@
+/*
+ * SPDX-FileCopyrightText: 2026 Coffey Labs LLC
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+import { describe, it, expect } from 'vitest';
+import { sha256 } from './sha256';
+
+const hex = (bytes: Uint8Array) => Array.from(bytes, (b) => b.toString(16).padStart(2, '0')).join('');
+const digest = (s: string) => hex(sha256(new TextEncoder().encode(s)));
+
+describe('sha256', () => {
+  // Digests from an independent implementation (Python's hashlib).
+  it.each([
+    ['', 'e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855'],
+    ['abc', 'ba7816bf8f01cfea414140de5dae2223b00361a396177a9cb410ff61f20015ad'],
+    [
+      'abcdbcdecdefdefgefghfghighijhijkijkljklmklmnlmnomnopnopq',
+      '248d6a61d20638b8e5c026930c3e6039a33ce45964ff2167f6ecedd419db06c1',
+    ],
+    ['ünïcödé ✓', 'aec840a69bab19009d54142263564850641d84635514a193da3948f5de76178c'],
+  ])('hashes %j', (input, expected) => {
+    expect(digest(input)).toBe(expected);
+  });
+
+  // 55 bytes is the most that pads into one block; 56 and 64 need a second.
+  it.each([
+    [55, '9f4390f8d30c2dd92ec9f095b65e2b9ae9b0a925a5258e241c9f1e910f734318'],
+    [56, 'b35439a4ac6f0948b6d6f9e3c6af0f5f590ce20f1bde7090ef7970686ec6738a'],
+    [64, 'ffe054fe7ae0cb6dc65c3af9b61d5209f439851db43d0ba5997337df154668eb'],
+    [1000, '41edece42d63e8d9bf515a9ba6932e1c20cbc9f5a5d134645adb5db1b9737ea3'],
+  ])('hashes %i bytes across the block boundary', (length, expected) => {
+    expect(digest('a'.repeat(length))).toBe(expected);
+  });
+
+  it('matches crypto.subtle on random input', async () => {
+    for (const length of [1, 43, 63, 65, 128, 300]) {
+      const data = crypto.getRandomValues(new Uint8Array(length));
+      const expected = new Uint8Array(await crypto.subtle.digest('SHA-256', data));
+      expect(hex(sha256(data))).toBe(hex(expected));
+    }
+  });
+});

src/lib/sha256.ts

@@ -0,0 +1,78 @@
+/*
+ * SPDX-FileCopyrightText: 2026 Coffey Labs LLC
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+// SHA-256 (FIPS 180-4) for pages served over plain HTTP, where browsers
+// leave out crypto.subtle. Sign-in needs it for the PKCE challenge, so the
+// console never has to fall back to sending the verifier itself.
+
+// The first 32 bits of the fractional parts of the cube roots of the first
+// 64 primes.
+const K = new Uint32Array([
+  0x428a2f98, 0x71374491, 0xb5c0fbcf, 0xe9b5dba5, 0x3956c25b, 0x59f111f1, 0x923f82a4, 0xab1c5ed5,
+  0xd807aa98, 0x12835b01, 0x243185be, 0x550c7dc3, 0x72be5d74, 0x80deb1fe, 0x9bdc06a7, 0xc19bf174,
+  0xe49b69c1, 0xefbe4786, 0x0fc19dc6, 0x240ca1cc, 0x2de92c6f, 0x4a7484aa, 0x5cb0a9dc, 0x76f988da,
+  0x983e5152, 0xa831c66d, 0xb00327c8, 0xbf597fc7, 0xc6e00bf3, 0xd5a79147, 0x06ca6351, 0x14292967,
+  0x27b70a85, 0x2e1b2138, 0x4d2c6dfc, 0x53380d13, 0x650a7354, 0x766a0abb, 0x81c2c92e, 0x92722c85,
+  0xa2bfe8a1, 0xa81a664b, 0xc24b8b70, 0xc76c51a3, 0xd192e819, 0xd6990624, 0xf40e3585, 0x106aa070,
+  0x19a4c116, 0x1e376c08, 0x2748774c, 0x34b0bcb5, 0x391c0cb3, 0x4ed8aa4a, 0x5b9cca4f, 0x682e6ff3,
+  0x748f82ee, 0x78a5636f, 0x84c87814, 0x8cc70208, 0x90befffa, 0xa4506ceb, 0xbef9a3f7, 0xc67178f2,
+]);
+
+// The first 32 bits of the fractional parts of the square roots of the
+// first 8 primes.
+const H0 = [0x6a09e667, 0xbb67ae85, 0x3c6ef372, 0xa54ff53a, 0x510e527f, 0x9b05688c, 0x1f83d9ab, 0x5be0cd19];
+
+const rotr = (x: number, n: number) => (x >>> n) | (x << (32 - n));
+
+export function sha256(data: Uint8Array): Uint8Array {
+  // The message, a 1 bit, zeros, and its length in bits as 64 bits, filling
+  // whole 64-byte blocks.
+  const blocks = new Uint8Array(Math.ceil((data.length + 9) / 64) * 64);
+  blocks.set(data);
+  blocks[data.length] = 0x80;
+  const view = new DataView(blocks.buffer);
+  const bits = data.length * 8;
+  view.setUint32(blocks.length - 8, Math.floor(bits / 0x100000000));
+  view.setUint32(blocks.length - 4, bits >>> 0);
+
+  const h = H0.slice();
+  const w = new Uint32Array(64);
+  for (let offset = 0; offset < blocks.length; offset += 64) {
+    for (let i = 0; i < 16; i++) w[i] = view.getUint32(offset + i * 4);
+    for (let i = 16; i < 64; i++) {
+      const s0 = rotr(w[i - 15], 7) ^ rotr(w[i - 15], 18) ^ (w[i - 15] >>> 3);
+      const s1 = rotr(w[i - 2], 17) ^ rotr(w[i - 2], 19) ^ (w[i - 2] >>> 10);
+      w[i] = (w[i - 16] + s0 + w[i - 7] + s1) >>> 0;
+    }
+
+    let [a, b, c, d, e, f, g, hh] = h;
+    for (let i = 0; i < 64; i++) {
+      const t1 = (hh + (rotr(e, 6) ^ rotr(e, 11) ^ rotr(e, 25)) + ((e & f) ^ (~e & g)) + K[i] + w[i]) >>> 0;
+      const t2 = ((rotr(a, 2) ^ rotr(a, 13) ^ rotr(a, 22)) + ((a & b) ^ (a & c) ^ (b & c))) >>> 0;
+      hh = g;
+      g = f;
+      f = e;
+      e = (d + t1) >>> 0;
+      d = c;
+      c = b;
+      b = a;
+      a = (t1 + t2) >>> 0;
+    }
+    h[0] = (h[0] + a) >>> 0;
+    h[1] = (h[1] + b) >>> 0;
+    h[2] = (h[2] + c) >>> 0;
+    h[3] = (h[3] + d) >>> 0;
+    h[4] = (h[4] + e) >>> 0;
+    h[5] = (h[5] + f) >>> 0;
+    h[6] = (h[6] + g) >>> 0;
+    h[7] = (h[7] + hh) >>> 0;
+  }
+
+  const out = new Uint8Array(32);
+  const outView = new DataView(out.buffer);
+  h.forEach((word, i) => outView.setUint32(i * 4, word));
+  return out;
+}

src/services/auth/oauth.test.ts

@@ -87,16 +87,19 @@ describe('generateCodeChallenge', () => {
     expect(challenge).toHaveLength(43);
   });
 
-  it('falls back to plain when crypto.subtle is unavailable', async () => {
+  it('still uses S256, with the same challenge, when crypto.subtle is unavailable', async () => {
+    const verifier = generateCodeVerifier();
+    const withSubtle = await generateCodeChallenge(verifier);
     const originalSubtle = crypto.subtle;
     Object.defineProperty(crypto, 'subtle', {
       configurable: true,
       get: () => undefined,
     });
     try {
-      const { challenge, method } = await generateCodeChallenge('plain-verifier');
-      expect(method).toBe('plain');
-      expect(challenge).toBe('plain-verifier');
+      const { challenge, method } = await generateCodeChallenge(verifier);
+      expect(method).toBe('S256');
+      expect(challenge).toBe(withSubtle.challenge);
+      expect(challenge).not.toBe(verifier);
     } finally {
       Object.defineProperty(crypto, 'subtle', {
         configurable: true,

src/services/auth/oauth.ts

@@ -10,6 +10,7 @@
 import { getApiBaseUrl } from '@/services/api';
 import { getBasePath } from '@/lib/basePath';
 import { getOAuthClientId } from '@/lib/oauthClientId';
+import { sha256 } from '@/lib/sha256';
 import i18n from '@/i18n';
 
 const SCOPES = import.meta.env.VITE_OAUTH_SCOPES as string | undefined;
@@ -82,17 +83,16 @@ export function generateCodeVerifier(length: number = 64): string {
   return out.join('');
 }
 
-export async function generateCodeChallenge(
-  verifier: string,
-): Promise<{ challenge: string; method: 'S256' | 'plain' }> {
-  if (typeof crypto === 'undefined' || typeof crypto.subtle === 'undefined') {
-    return { challenge: verifier, method: 'plain' };
-  }
-
-  const encoder = new TextEncoder();
-  const data = encoder.encode(verifier);
-  const digest = await crypto.subtle.digest('SHA-256', data);
-  return { challenge: base64UrlEncode(new Uint8Array(digest)), method: 'S256' };
+// inbuxa: always S256. Over plain HTTP, where browsers leave out
+// crypto.subtle, the digest comes from our own SHA-256 instead of falling
+// back to `plain`, which would send the verifier itself as the challenge.
+export async function generateCodeChallenge(verifier: string): Promise<{ challenge: string; method: 'S256' }> {
+  const data = new TextEncoder().encode(verifier);
+  const digest =
+    typeof crypto !== 'undefined' && typeof crypto.subtle !== 'undefined'
+      ? new Uint8Array(await crypto.subtle.digest('SHA-256', data))
+      : sha256(data);
+  return { challenge: base64UrlEncode(digest), method: 'S256' };
 }
 
 function generateState(): string {