diff --git a/app/middleware/auth.js b/app/middleware/auth.js
index 4b6bedf..42946e9 100644
--- a/app/middleware/auth.js
+++ b/app/middleware/auth.js
@@ -27,16 +27,33 @@
  *   keeps the cheap check cheap (one DB hit, not three).
  */
 
+const crypto = require('crypto');
 const { sequelize } = require('../config/db.config.js');
 const db = require('../config/db.config.js');
 const log = require('../config/logger.js');
 
+/**
+ * Hash an authKey for lookup. Migration 20260518000000 converted
+ * ApiKey.akKEY / ApiMaster.amKEY columns from UUID to TEXT and
+ * replaced row values with SHA-256 hex digests. Operator tokens
+ * issued before the migration keep working because the API hashes
+ * the incoming header here before the SQL lookup.
+ *
+ * SHA-256 unsalted (vs bcrypt/argon2id) because API tokens are
+ * high-entropy (UUID v4 = 122 bits); brute force against a leaked
+ * hash table is impractical. Hashing is to prevent direct replay
+ * if the DB leaks, not to protect a low-entropy password.
+ */
+function hashKey(rawKey) {
+    return crypto.createHash('sha256').update(String(rawKey)).digest('hex');
+}
+
 async function isMaster(authKey) {
     if (!authKey || authKey.length === 0) return false;
     try {
         const r = await db.sequelize.query(
             'SELECT * FROM "dbo"."ApiMaster" WHERE "amKEY" = ? AND "ApiMaster"."amArchive" = false;',
-            { replacements: [authKey], type: sequelize.QueryTypes.SELECT },
+            { replacements: [hashKey(authKey)], type: sequelize.QueryTypes.SELECT },
         );
         if (!r || r.length === 0) return false;
         return typeof r[0].amId === 'number' && r[0].amId > 0;
@@ -51,7 +68,7 @@ async function getCompanyId(authKey) {
     try {
         const r = await db.sequelize.query(
             'SELECT * FROM "dbo"."ApiKey" WHERE "akKEY" = ? AND "ApiKey"."akArchive" = false;',
-            { replacements: [authKey], type: sequelize.QueryTypes.SELECT },
+            { replacements: [hashKey(authKey)], type: sequelize.QueryTypes.SELECT },
         );
         if (!r || r.length === 0) return -1;
         const cid = r[0].akCompanyId;
@@ -220,4 +237,5 @@ module.exports = {
     getCompanyIdByPohId,
     requireAuthKey,
     resolveAuth,
+    hashKey,
 };
diff --git a/app/migrations/20260518000000-hash-api-keys.js b/app/migrations/20260518000000-hash-api-keys.js
new file mode 100644
index 0000000..2da97d8
--- /dev/null
+++ b/app/migrations/20260518000000-hash-api-keys.js
@@ -0,0 +1,134 @@
+// SPDX-License-Identifier: Apache-2.0
+// Copyright 2026 Aaron K. Clark
+//
+// Hash ApiKey.akKEY + ApiMaster.amKEY at rest.
+//
+// Background (audit issue #73, P1-A):
+//   The two key columns were UUID-typed and stored the raw token
+//   verbatim. Any DB leak or read-replica snapshot meant every
+//   active operator's credential was immediately usable. After
+//   this migration the columns store a SHA-256 hex digest of the
+//   raw token; auth.js hashes the incoming header before lookup,
+//   so operator-held tokens keep working without re-issue.
+//
+// Migration steps:
+//   1. Change column types from UUID to TEXT (USING cast() so PG
+//      doesn't error on existing rows). Drop NOT NULL temporarily
+//      so we can write the hash without race-conditions on length.
+//   2. UPDATE each row's <key> to SHA256(<old value>) in JS.
+//      Skip rows whose value is already 64 hex chars (operator
+//      may have run a partial migration manually).
+//   3. Re-apply NOT NULL.
+//
+// Rollback (down):
+//   Cannot recover plaintext from a SHA-256 hash. The down step
+//   only reverts the column TYPE to UUID; rows will then need to
+//   be manually rotated. Document that operationally.
+
+'use strict';
+
+const crypto = require('crypto');
+
+function sha256(s) {
+    return crypto.createHash('sha256').update(String(s)).digest('hex');
+}
+
+module.exports = {
+    async up(queryInterface, Sequelize) {
+        const SCHEMA = 'dbo';
+        const sequelize = queryInterface.sequelize;
+
+        // --- ApiKey ---
+        await sequelize.query(
+            `ALTER TABLE "${SCHEMA}"."ApiKey"
+                ALTER COLUMN "akKEY" DROP NOT NULL`,
+        );
+        await sequelize.query(
+            `ALTER TABLE "${SCHEMA}"."ApiKey"
+                ALTER COLUMN "akKEY" TYPE TEXT USING "akKEY"::text`,
+        );
+
+        const apiKeyRows = await sequelize.query(
+            `SELECT "akId", "akKEY" FROM "${SCHEMA}"."ApiKey"`,
+            { type: Sequelize.QueryTypes.SELECT },
+        );
+        for (const r of apiKeyRows) {
+            const v = r.akKEY || '';
+            // Skip already-hashed rows: SHA-256 hex is exactly 64 chars and
+            // matches /^[0-9a-f]+$/. Real UUIDs (36 chars w/ dashes) don't.
+            if (v.length === 64 && /^[0-9a-f]+$/.test(v)) continue;
+            const hashed = sha256(v);
+            await sequelize.query(
+                `UPDATE "${SCHEMA}"."ApiKey" SET "akKEY" = :hashed WHERE "akId" = :id`,
+                { replacements: { hashed, id: r.akId } },
+            );
+        }
+
+        await sequelize.query(
+            `ALTER TABLE "${SCHEMA}"."ApiKey"
+                ALTER COLUMN "akKEY" SET NOT NULL`,
+        );
+        // Index the hashed key so WHERE "akKEY" = ? lookups stay
+        // fast. Non-unique on purpose: archived rows from key
+        // rotation may share a hash with their non-archived
+        // replacement until they're physically deleted, and uniqueness
+        // was never enforced as a constraint pre-migration.
+        await sequelize.query(
+            `CREATE INDEX IF NOT EXISTS "ApiKey_keyHash_idx" ON "${SCHEMA}"."ApiKey" ("akKEY")`,
+        );
+
+        // --- ApiMaster ---
+        await sequelize.query(
+            `ALTER TABLE "${SCHEMA}"."ApiMaster"
+                ALTER COLUMN "amKEY" DROP NOT NULL`,
+        );
+        await sequelize.query(
+            `ALTER TABLE "${SCHEMA}"."ApiMaster"
+                ALTER COLUMN "amKEY" TYPE TEXT USING "amKEY"::text`,
+        );
+
+        const apiMasterRows = await sequelize.query(
+            `SELECT "amId", "amKEY" FROM "${SCHEMA}"."ApiMaster"`,
+            { type: Sequelize.QueryTypes.SELECT },
+        );
+        for (const r of apiMasterRows) {
+            const v = r.amKEY || '';
+            if (v.length === 64 && /^[0-9a-f]+$/.test(v)) continue;
+            const hashed = sha256(v);
+            await sequelize.query(
+                `UPDATE "${SCHEMA}"."ApiMaster" SET "amKEY" = :hashed WHERE "amId" = :id`,
+                { replacements: { hashed, id: r.amId } },
+            );
+        }
+
+        await sequelize.query(
+            `ALTER TABLE "${SCHEMA}"."ApiMaster"
+                ALTER COLUMN "amKEY" SET NOT NULL`,
+        );
+        await sequelize.query(
+            `CREATE INDEX IF NOT EXISTS "ApiMaster_keyHash_idx" ON "${SCHEMA}"."ApiMaster" ("amKEY")`,
+        );
+    },
+
+    async down(queryInterface, Sequelize) {
+        const SCHEMA = 'dbo';
+        const sequelize = queryInterface.sequelize;
+
+        // Drop the lookup indexes first; can't change column type while
+        // an index references it.
+        await sequelize.query(`DROP INDEX IF EXISTS "${SCHEMA}"."ApiKey_keyHash_idx"`);
+        await sequelize.query(`DROP INDEX IF EXISTS "${SCHEMA}"."ApiMaster_keyHash_idx"`);
+
+        // Convert TYPE back to UUID. Any rows whose current value is a
+        // SHA-256 hex string will fail the cast — the operator has to
+        // rotate them to fresh UUIDs first.
+        await sequelize.query(
+            `ALTER TABLE "${SCHEMA}"."ApiKey"
+                ALTER COLUMN "akKEY" TYPE uuid USING "akKEY"::uuid`,
+        );
+        await sequelize.query(
+            `ALTER TABLE "${SCHEMA}"."ApiMaster"
+                ALTER COLUMN "amKEY" TYPE uuid USING "amKEY"::uuid`,
+        );
+    },
+};
diff --git a/tests/unit/auth-hash.test.js b/tests/unit/auth-hash.test.js
new file mode 100644
index 0000000..14a9417
--- /dev/null
+++ b/tests/unit/auth-hash.test.js
@@ -0,0 +1,57 @@
+// SPDX-License-Identifier: Apache-2.0
+// Copyright 2026 Aaron K. Clark
+//
+// Unit tests for auth.hashKey + the short-circuit paths of
+// isMaster / getCompanyId.
+//
+// We can't drive the "hashed value reaches the SQL query" assertion
+// from here because vi.mock on db.config.js doesn't intercept the
+// nested CJS require chain inside auth.js (documented in audit
+// issue #73 P5-M). Behavioral coverage of the hash-on-lookup path
+// lives in the integration suite; what this file verifies is the
+// pure-Node hash logic + the no-DB short-circuit paths.
+
+import { describe, test, expect } from 'vitest';
+
+const { hashKey, isMaster, getCompanyId } = require('../../app/middleware/auth.js');
+
+describe('auth.hashKey', () => {
+    test('returns a 64-char lowercase hex SHA-256 digest', () => {
+        const h = hashKey('any-token');
+        expect(h).toMatch(/^[0-9a-f]{64}$/);
+    });
+
+    test('deterministic: same input → same hash', () => {
+        expect(hashKey('abc')).toBe(hashKey('abc'));
+    });
+
+    test('different inputs → different hashes', () => {
+        expect(hashKey('abc')).not.toBe(hashKey('abd'));
+    });
+
+    test('known vector: sha256("") matches RFC reference', () => {
+        // Empty-string SHA-256: e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855
+        expect(hashKey('')).toBe('e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855');
+    });
+
+    test('handles non-string input via String() coercion', () => {
+        expect(() => hashKey(12345)).not.toThrow();
+        expect(hashKey(12345)).toBe(hashKey('12345'));
+    });
+});
+
+describe('auth.isMaster — short-circuit paths', () => {
+    test('returns false on empty / null input without hitting the DB', async () => {
+        expect(await isMaster('')).toBe(false);
+        expect(await isMaster(null)).toBe(false);
+        expect(await isMaster(undefined)).toBe(false);
+    });
+});
+
+describe('auth.getCompanyId — short-circuit paths', () => {
+    test('returns -1 sentinel on empty / null input without hitting the DB', async () => {
+        expect(await getCompanyId('')).toBe(-1);
+        expect(await getCompanyId(null)).toBe(-1);
+        expect(await getCompanyId(undefined)).toBe(-1);
+    });
+});