Inline OAuth2 signing key in config

The OAuth2/OIDC server accepted its signing key via a file path
(key-file), while every other PEM key in the probod config (SAML
private key, ACME account key) is embedded inline. Switch the
field to a private-key string so the convention is uniform.

The signing key is operator-supplied material that must outlive
any process restart, so the bootstrap builder now treats
OAUTH2_SERVER_SIGNING_KEY as required and refuses to start
without one; silently minting a fresh key per boot would break
token validation across rollouts. The OAUTH2_SERVER_* env vars
otherwise flow through builder.Build like the existing SAML
block so the new OAuth2Server section is populated end-to-end.

Rework the e2e harness to render its config via bootstrap at
test setup, which removes the static
e2e/console/testdata/config.yaml and the previously generated
test-only PEM file. A per-run RSA key is minted via
bootstrap.GenerateOAuth2SigningKey (kept public for test
tooling) and injected through the builder env map. CI now
passes ACME_ROOT_CA inline instead of mutating a YAML on disk.

Signed-off-by: Bryan Frimin <bryan@getprobo.com>

.github/workflows/make.yaml

@@ -401,29 +401,14 @@ jobs:
           SKIP_APPS=1 make bin/probod
           wait $STACK_PID
       - run: "make stack-ps"
-      - name: "Inject root CA into e2e config"
-        run: |
-          python3 << 'EOF'
-          import yaml
-
-          with open('compose/pebble/certs/rootCA.pem', 'r') as f:
-              root_ca = f.read()
-
-          with open('e2e/console/testdata/config.yaml', 'r') as f:
-              config = yaml.safe_load(f)
-
-          config['probod']['custom-domains']['acme']['root-ca'] = root_ca
-
-          with open('e2e/console/testdata/config.yaml', 'w') as f:
-              yaml.dump(config, f, default_flow_style=False, allow_unicode=True)
-          EOF
       - name: "Run e2e tests"
         env:
           PROBO_E2E_BINARY: "${{ github.workspace }}/bin/probod"
-          PROBO_E2E_CONFIG: "${{ github.workspace }}/e2e/console/testdata/config.yaml"
           GOTESTSUM_FORMAT: "testname"
           GOTESTSUM_JUNITFILE: "junit-e2e.xml"
-        run: "CGO_ENABLED=1 go tool gotestsum -- -race -cover -coverprofile=coverage.out -count=1 ./e2e/console/..."
+        run: |
+          ACME_ROOT_CA="$(cat compose/pebble/certs/rootCA.pem)" \
+            CGO_ENABLED=1 go tool gotestsum -- -race -cover -coverprofile=coverage.out -count=1 ./e2e/console/...
       - name: "Upload test results"
         uses: "actions/upload-artifact@bbbca2ddaa5d8feaa63e36b76fdaad77386f024f" # v7
         if: "always()"

GNUmakefile

@@ -38,7 +38,6 @@ GO_TOOL=	$(GO_BASE) tool
 
 TEST_FLAGS?=	-race -cover -coverprofile=coverage.out
 
-E2E_CONFIG ?= $(CURDIR)/e2e/console/testdata/config.yaml
 E2E_COVER_DIR ?= $(CURDIR)/coverage/e2e
 
 DOCKER_IMAGE_NAME=	ghcr.io/getprobo/probo
@@ -129,7 +128,6 @@ test-bench: test ## Run benchmark tests
 test-e2e: CGO_ENABLED=1
 test-e2e: bin/probod ## Run console e2e tests
 	PROBO_E2E_BINARY=$(CURDIR)/bin/probod \
-	PROBO_E2E_CONFIG=$(E2E_CONFIG) \
 	GOTESTSUM_FORMAT=testname $(GO_TEST) -count=1 ./e2e/console/...
 
 bin/probod-coverage:
@@ -140,7 +138,6 @@ test-e2e-coverage: bin/probod-coverage ## Run e2e tests with coverage
 	@$(RM) -rf $(E2E_COVER_DIR) && $(MKDIR) -p $(E2E_COVER_DIR)
 	PROBO_E2E_BINARY=$(CURDIR)/bin/probod-coverage \
 	PROBO_E2E_COVERDIR=$(E2E_COVER_DIR) \
-	PROBO_E2E_CONFIG=$(E2E_CONFIG) \
 	CGO_ENABLED=1 $(GO) test -count=1 -v ./e2e/console/...
 	$(GO) tool covdata textfmt -i=$(E2E_COVER_DIR) -o=coverage-e2e.out
 	$(GO) tool cover -html=coverage-e2e.out -o=coverage-e2e.html

contrib/claude/config.md

@@ -11,7 +11,7 @@ When a configuration field is added, renamed, or removed in the Go config struct
 | 3 | `pkg/bootstrap/builder.go` | Env-var → struct mapping (`Build()` method) |
 | 4 | `pkg/bootstrap/builder.go` | Required-env validation (`validateRequired()`) |
 | 5 | `cfg/dev.yaml` | Local development config |
-| 6 | `e2e/console/testdata/config.yaml` | E2E test config |
+| 6 | `e2e/internal/testutil/testutil.go` | E2E env-var map fed to `bootstrap.NewBuilder` |
 | 7 | `contrib/lima/provision.sh` | Sandbox env vars passed to `probod-bootstrap` |
 | 8 | `contrib/helm/charts/probo/values.yaml` | Helm default values |
 | 9 | `contrib/helm/charts/probo/values-production.yaml.example` | Helm production template |
@@ -28,7 +28,7 @@ Go struct (pkg/probod/)
   ├─► bootstrap builder.go (env var → struct)
   │     │
   │     ├─► cfg/dev.yaml              (static YAML, local dev)
-  │     ├─► e2e/console/testdata/     (static YAML, tests)
+  │     ├─► e2e/internal/testutil/    (env map → bootstrap.Build, tests)
   │     ├─► contrib/lima/provision.sh  (env vars → probod-bootstrap)
   │     └─► Helm chart
   │           ├─ values.yaml           (user-facing knobs)
@@ -45,7 +45,7 @@ Go struct (pkg/probod/)
 2. **Env var naming** — follow the existing convention in `builder.go`: `SECTION_FIELD_NAME` (e.g. `AUTH_COOKIE_DOMAIN`, `CUSTOM_DOMAINS_RENEWAL_INTERVAL`).
 3. **Secrets** go through `secret.yaml` and are referenced via `secretKeyRef` in `deployment.yaml`. Non-secret values are set inline.
 4. **`cfg/dev.yaml`** uses safe, non-production defaults (plaintext passwords, `localhost`, `secure: false`).
-5. **`e2e/console/testdata/config.yaml`** mirrors `cfg/dev.yaml` but with test-specific values (different ports, `probod_test` DB, shorter intervals).
+5. **`e2e/internal/testutil/testutil.go`** builds the e2e config through `bootstrap.NewBuilder` with a test-only env-var map (different ports, `probod_test` DB, shorter intervals). Any new field whose test value differs from the bootstrap default must be added to that map.
 6. **`provision.sh`** only sets env vars that differ from `builder.go` defaults (e.g. `PROBOD_BASE_URL`, `AUTH_COOKIE_DOMAIN`, `AUTH_COOKIE_SECURE`). If the new field's default is acceptable in the sandbox, no env var is needed.
 7. **Helm `values.yaml`** exposes the field under the appropriate `probo.*` key with a sensible default. `values-production.yaml.example` includes it only when the production value differs or the user must set it.
 8. **Optional features** (custom domains, SAML, connectors, tracing) are gated by `{{- if }}` blocks in the Helm templates; follow the same pattern for new optional fields.

contrib/claude/make.md

@@ -78,4 +78,3 @@ The project uses a `GNUmakefile` at the root. Builds run with `--jobs=$(nproc)`
 | `GOOS` | (host) | Cross-compile target OS |
 | `TEST_FLAGS` | `-race -cover -coverprofile=coverage.out` | Extra flags passed to `go test` |
 | `DOCKER_BUILD_FLAGS` | (empty) | Extra flags for `docker build` |
-| `E2E_CONFIG` | `e2e/console/testdata/config.yaml` | E2E test config path |

e2e/console/testdata/config.yaml

@@ -1,99 +0,0 @@
-unit:
-  metrics:
-    addr: "localhost:19081"
-  tracing:
-    addr: "localhost:14317"
-    max-batch-size: 512
-    batch-timeout: 5
-    export-timeout: 30
-    max-queue-size: 2048
-
-probod:
-  base-url: "http://localhost:18080"
-  encryption-key: "thisisnotasecretAAAAAAAAAAAAAAAAAAAAAAAAAAA="
-  chrome-dp-addr: "localhost:9222"
-
-  api:
-    addr: "localhost:18080"
-    cors:
-      allowed-origins: ["http://localhost:18080"]
-    extra-header-fields: {}
-
-  pg:
-    addr: "localhost:5432"
-    username: "postgres"
-    password: "postgres"
-    database: "probod_test"
-    pool-size: 10
-
-  auth:
-    disable-signup: false
-    invitation-confirmation-token-validity: 3600
-    cookie:
-      name: "SSID"
-      domain: "localhost"
-      secret: "this-is-a-secure-secret-for-cookie-signing-at-least-32-bytes"
-      duration: 24
-      secure: false
-    password:
-      pepper: "this-is-a-secure-pepper-for-password-hashing-at-least-32-bytes"
-      iterations: 600000
-    oauth2-server:
-      signing-keys:
-        - key-file: "./testdata/oauth2_signing_key.pem"
-          kid: "test-key-1"
-          active: true
-      access-token-duration: 10
-      refresh-token-duration: 10
-      authorization-code-duration: 5
-      device-code-duration: 15
-
-  trust-center:
-    http-addr: ":10080"
-    https-addr: ":10443"
-
-  aws:
-    region: "us-east-1"
-    bucket: "probod-test"
-    access-key-id: "probod"
-    secret-access-key: "thisisnotasecret"
-    endpoint: "http://127.0.0.1:8333"
-
-  notifications:
-    mailer:
-      sender-name: "Probo Test"
-      sender-email: "no-reply@test.getprobo.com"
-      smtp:
-        addr: "localhost:1025"
-        tls-required: false
-      mailer-interval: 1
-    slack:
-      sender-interval: 60
-
-  llm:
-    providers:
-      openai:
-        type: "openai"
-        api-key: "thisisnotasecret"
-    defaults:
-      provider: "openai"
-      model-name: "gpt-4o"
-      temperature: 0.1
-      max-tokens: 4096
-
-  evidence-describer:
-    interval: 10
-    stale-after: 300
-    max-concurrency: 10
-
-  custom-domains:
-    renewal-interval: 3600
-    provision-interval: 30
-    cname-target: "custom.test.getprobo.com"
-    acme:
-      directory: "https://localhost:14000/dir"
-      email: "admin@test.getprobo.com"
-      key-type: "EC256"
-      root-ca: ""
-
-  connectors: []

e2e/internal/testutil/testutil.go

@@ -17,20 +17,18 @@ package testutil
 import (
 	"bytes"
 	"context"
-	"crypto/rand"
-	"crypto/rsa"
-	"crypto/x509"
-	"encoding/pem"
 	"fmt"
 	"io"
 	"net/http"
 	"os"
 	"os/exec"
+	"path/filepath"
 	"sync"
 	"syscall"
 	"time"
 
 	"go.gearno.de/kit/log"
+	"go.probo.inc/probo/pkg/bootstrap"
 )
 
 var (
@@ -68,7 +66,6 @@ func (s *switchableWriter) switchTo(w io.Writer) {
 func Setup() {
 	setupOnce.Do(func() {
 		binaryPath := os.Getenv("PROBO_E2E_BINARY")
-		configPath := os.Getenv("PROBO_E2E_CONFIG")
 		coverDir := os.Getenv("PROBO_E2E_COVERDIR")
 
 		if binaryPath == "" {
@@ -76,11 +73,6 @@ func Setup() {
 			os.Exit(1)
 		}
 
-		if configPath == "" {
-			fmt.Fprintf(os.Stderr, "e2etest: PROBO_E2E_CONFIG is required\n")
-			os.Exit(1)
-		}
-
 		// Create coverage directory if specified
 		if coverDir != "" {
 			if err := os.MkdirAll(coverDir, 0755); err != nil {
@@ -89,8 +81,9 @@ func Setup() {
 			}
 		}
 
-		if err := ensureSigningKey("./testdata/oauth2_signing_key.pem"); err != nil {
+		configPath, err := generateConfig()
-			fmt.Fprintf(os.Stderr, "e2etest: cannot create signing key: %v\n", err)
+		if err != nil {
+			fmt.Fprintf(os.Stderr, "e2etest: cannot generate config: %v\n", err)
 			os.Exit(1)
 		}
 
@@ -241,30 +234,93 @@ func GetMailpitBaseURL() string {
 	return testEnv.MailpitBaseURL
 }
 
-// ensureSigningKey creates a 2048-bit RSA PEM key at path if it does not
+// generateConfig builds a probod config for the e2e suite via the
-// already exist. The key is used exclusively for e2e test JWT signing.
+// bootstrap package (which auto-generates SAML credentials) and
-func ensureSigningKey(path string) error {
+// writes it to a temp file. A fresh OAuth2 signing key is minted
-	if _, err := os.Stat(path); err == nil {
+// here and injected via env. Returns the path.
-		return nil
+func generateConfig() (string, error) {
-	}
+	oauth2SigningKey, err := bootstrap.GenerateOAuth2SigningKey()
-
-	key, err := rsa.GenerateKey(rand.Reader, 2048)
 	if err != nil {
-		return fmt.Errorf("cannot generate RSA key: %w", err)
+		return "", fmt.Errorf("generate oauth2 signing key: %w", err)
 	}
 
-	data := pem.EncodeToMemory(&pem.Block{
+	env := map[string]string{
-		Type:  "RSA PRIVATE KEY",
+		// Required.
-		Bytes: x509.MarshalPKCS1PrivateKey(key),
+		"PROBOD_ENCRYPTION_KEY":     "thisisnotasecretAAAAAAAAAAAAAAAAAAAAAAAAAAA=",
+		"AUTH_COOKIE_SECRET":        "this-is-a-secure-secret-for-cookie-signing-at-least-32-bytes",
+		"AUTH_PASSWORD_PEPPER":      "this-is-a-secure-pepper-for-password-hashing-at-least-32-bytes",
+		"OAUTH2_SERVER_SIGNING_KEY": oauth2SigningKey,
+
+		// Unit.
+		"METRICS_ADDR": "localhost:19081",
+		"TRACING_ADDR": "localhost:14317",
+
+		// Probod base.
+		"PROBOD_BASE_URL": "http://localhost:18080",
+
+		// API.
+		"API_ADDR":                 "localhost:18080",
+		"API_CORS_ALLOWED_ORIGINS": "http://localhost:18080",
+
+		// PG.
+		"PG_DATABASE":  "probod_test",
+		"PG_POOL_SIZE": "10",
+
+		// Auth.
+		"AUTH_COOKIE_SECURE":       "false",
+		"AUTH_PASSWORD_ITERATIONS": "600000",
+
+		// OAuth2 server durations kept small for faster e2e flows.
+		"OAUTH2_SERVER_ACCESS_TOKEN_DURATION":       "10",
+		"OAUTH2_SERVER_REFRESH_TOKEN_DURATION":      "10",
+		"OAUTH2_SERVER_AUTHORIZATION_CODE_DURATION": "5",
+		"OAUTH2_SERVER_DEVICE_CODE_DURATION":        "15",
+
+		// Trust center.
+		"TRUST_CENTER_HTTP_ADDR":  ":10080",
+		"TRUST_CENTER_HTTPS_ADDR": ":10443",
+
+		// AWS / S3 (SeaweedFS).
+		"AWS_BUCKET":            "probod-test",
+		"AWS_ACCESS_KEY_ID":     "probod",
+		"AWS_SECRET_ACCESS_KEY": "thisisnotasecret",
+		"AWS_ENDPOINT":          "http://127.0.0.1:8333",
+
+		// Mailer.
+		"MAILER_SENDER_NAME":  "Probo Test",
+		"MAILER_SENDER_EMAIL": "no-reply@test.getprobo.com",
+		"MAILER_INTERVAL":     "1",
+
+		// LLM.
+		"OPENAI_API_KEY": "thisisnotasecret",
+
+		// Custom domains.
+		"CUSTOM_DOMAINS_CNAME_TARGET": "custom.test.getprobo.com",
+		"ACME_DIRECTORY":              "https://localhost:14000/dir",
+		"ACME_EMAIL":                  "admin@test.getprobo.com",
+	}
+
+	builder := bootstrap.NewBuilder(func(key string) string {
+		if v, ok := env[key]; ok {
+			return v
+		}
+		return os.Getenv(key)
 	})
 
-	if err := os.MkdirAll("testdata", 0755); err != nil {
+	cfg, err := builder.Build()
-		return fmt.Errorf("cannot create testdata directory: %w", err)
+	if err != nil {
+		return "", fmt.Errorf("build config: %w", err)
 	}
 
-	if err := os.WriteFile(path, data, 0600); err != nil {
+	tmpDir, err := os.MkdirTemp("", "probo-e2e-")
-		return fmt.Errorf("cannot write key file: %w", err)
+	if err != nil {
+		return "", fmt.Errorf("create temp dir: %w", err)
+	}
+	path := filepath.Join(tmpDir, "probod.yml")
+
+	if err := bootstrap.WriteConfig(cfg, path); err != nil {
+		return "", fmt.Errorf("write config: %w", err)
 	}
 
-	return nil
+	return path, nil
 }

pkg/bootstrap/builder.go

@@ -26,9 +26,10 @@ import (
 type EnvGetter func(key string) string
 
 type Builder struct {
-	getEnv          EnvGetter
+	getEnv           EnvGetter
-	samlCertificate string
+	samlCertificate  string
-	samlPrivateKey  string
+	samlPrivateKey   string
+	oauth2SigningKey string
 }
 
 func NewBuilder(getEnv EnvGetter) *Builder {
@@ -48,6 +49,8 @@ func (b *Builder) Build() (*probod.FullConfig, error) {
 		return nil, fmt.Errorf("cannot get SAML credentials: %w", err)
 	}
 
+	oauth2SigningKey := b.getOAuth2SigningKey()
+
 	pgCACertBundle := b.getPgCACertBundle()
 
 	cfg := &probod.FullConfig{
@@ -120,6 +123,17 @@ func (b *Builder) Build() (*probod.FullConfig, error) {
 					ClientSecret: b.getEnv("AUTH_MICROSOFT_CLIENT_SECRET"),
 					Enabled:      b.getEnv("AUTH_MICROSOFT_CLIENT_ID") != "" && b.getEnv("AUTH_MICROSOFT_CLIENT_SECRET") != "",
 				},
+				OAuth2Server: probod.OAuth2ServerConfig{
+					SigningKeys: []probod.OAuth2SigningKeyConfig{{
+						PrivateKey: oauth2SigningKey,
+						KID:        b.getEnvOrDefault("OAUTH2_SERVER_SIGNING_KEY_KID", "default"),
+						Active:     true,
+					}},
+					AccessTokenDuration:       b.getEnvIntOrDefault("OAUTH2_SERVER_ACCESS_TOKEN_DURATION", 3600),
+					RefreshTokenDuration:      b.getEnvIntOrDefault("OAUTH2_SERVER_REFRESH_TOKEN_DURATION", 2592000),
+					AuthorizationCodeDuration: b.getEnvIntOrDefault("OAUTH2_SERVER_AUTHORIZATION_CODE_DURATION", 600),
+					DeviceCodeDuration:        b.getEnvIntOrDefault("OAUTH2_SERVER_DEVICE_CODE_DURATION", 600),
+				},
 			},
 			TrustCenter: probod.TrustCenterConfig{
 				HTTPAddr:  b.getEnvOrDefault("TRUST_CENTER_HTTP_ADDR", ":80"),
@@ -323,6 +337,10 @@ func (b *Builder) validateRequired() error {
 		}
 	}
 
+	if b.oauth2SigningKey == "" && b.getEnv("OAUTH2_SERVER_SIGNING_KEY") == "" {
+		missing = append(missing, "OAUTH2_SERVER_SIGNING_KEY")
+	}
+
 	if slackClientID := b.getEnv("CONNECTOR_SLACK_CLIENT_ID"); slackClientID != "" {
 		slackRequired := []string{
 			"CONNECTOR_SLACK_CLIENT_SECRET",
@@ -388,6 +406,13 @@ func (b *Builder) getSAMLCredentials() (cert, key string, err error) {
 	return cert, key, nil
 }
 
+func (b *Builder) getOAuth2SigningKey() string {
+	if b.oauth2SigningKey != "" {
+		return b.oauth2SigningKey
+	}
+	return b.getEnv("OAUTH2_SERVER_SIGNING_KEY")
+}
+
 func (b *Builder) getPgCACertBundle() string {
 	if path := b.getEnv("PG_CA_BUNDLE_PATH"); path != "" {
 		data, err := os.ReadFile(path)

pkg/bootstrap/builder_test.go

@@ -32,9 +32,10 @@ func mockEnv(env map[string]string) EnvGetter {
 
 func requiredEnv() map[string]string {
 	return map[string]string{
-		"PROBOD_ENCRYPTION_KEY": "test-encryption-key-32-bytes-long",
+		"PROBOD_ENCRYPTION_KEY":     "test-encryption-key-32-bytes-long",
-		"AUTH_COOKIE_SECRET":    "test-cookie-secret-32-bytes-long!",
+		"AUTH_COOKIE_SECRET":        "test-cookie-secret-32-bytes-long!",
-		"AUTH_PASSWORD_PEPPER":  "test-password-pepper-32-bytes-lo",
+		"AUTH_PASSWORD_PEPPER":      "test-password-pepper-32-bytes-lo",
+		"OAUTH2_SERVER_SIGNING_KEY": "test-oauth2-signing-key",
 	}
 }
 
@@ -47,7 +48,16 @@ func TestBuilder_Build_MissingRequiredEnvVars(t *testing.T) {
 		{
 			name:        "all missing",
 			env:         map[string]string{},
-			wantMissing: []string{"PROBOD_ENCRYPTION_KEY", "AUTH_COOKIE_SECRET", "AUTH_PASSWORD_PEPPER"},
+			wantMissing: []string{"PROBOD_ENCRYPTION_KEY", "AUTH_COOKIE_SECRET", "AUTH_PASSWORD_PEPPER", "OAUTH2_SERVER_SIGNING_KEY"},
+		},
+		{
+			name: "missing oauth2 signing key",
+			env: map[string]string{
+				"PROBOD_ENCRYPTION_KEY": "key",
+				"AUTH_COOKIE_SECRET":    "secret",
+				"AUTH_PASSWORD_PEPPER":  "pepper",
+			},
+			wantMissing: []string{"OAUTH2_SERVER_SIGNING_KEY"},
 		},
 		{
 			name: "missing encryption key",
@@ -415,6 +425,64 @@ func TestBuilder_Build_SAMLPreset(t *testing.T) {
 	assert.Equal(t, "preset-key", cfg.Probod.Auth.SAML.PrivateKey)
 }
 
+func TestBuilder_Build_OAuth2Defaults(t *testing.T) {
+	b := NewBuilder(mockEnv(requiredEnv()))
+
+	cfg, err := b.Build()
+	require.NoError(t, err)
+
+	require.Len(t, cfg.Probod.Auth.OAuth2Server.SigningKeys, 1)
+	sk := cfg.Probod.Auth.OAuth2Server.SigningKeys[0]
+	assert.Equal(t, "test-oauth2-signing-key", sk.PrivateKey)
+	assert.Equal(t, "default", sk.KID)
+	assert.True(t, sk.Active)
+
+	assert.Equal(t, 3600, cfg.Probod.Auth.OAuth2Server.AccessTokenDuration)
+	assert.Equal(t, 2592000, cfg.Probod.Auth.OAuth2Server.RefreshTokenDuration)
+	assert.Equal(t, 600, cfg.Probod.Auth.OAuth2Server.AuthorizationCodeDuration)
+	assert.Equal(t, 600, cfg.Probod.Auth.OAuth2Server.DeviceCodeDuration)
+}
+
+func TestBuilder_Build_OAuth2FromEnv(t *testing.T) {
+	env := requiredEnv()
+	env["OAUTH2_SERVER_SIGNING_KEY"] = "env-signing-key"
+	env["OAUTH2_SERVER_SIGNING_KEY_KID"] = "env-kid"
+	env["OAUTH2_SERVER_ACCESS_TOKEN_DURATION"] = "10"
+	env["OAUTH2_SERVER_REFRESH_TOKEN_DURATION"] = "20"
+	env["OAUTH2_SERVER_AUTHORIZATION_CODE_DURATION"] = "30"
+	env["OAUTH2_SERVER_DEVICE_CODE_DURATION"] = "40"
+
+	b := NewBuilder(mockEnv(env))
+
+	cfg, err := b.Build()
+	require.NoError(t, err)
+
+	require.Len(t, cfg.Probod.Auth.OAuth2Server.SigningKeys, 1)
+	sk := cfg.Probod.Auth.OAuth2Server.SigningKeys[0]
+	assert.Equal(t, "env-signing-key", sk.PrivateKey)
+	assert.Equal(t, "env-kid", sk.KID)
+	assert.True(t, sk.Active)
+
+	assert.Equal(t, 10, cfg.Probod.Auth.OAuth2Server.AccessTokenDuration)
+	assert.Equal(t, 20, cfg.Probod.Auth.OAuth2Server.RefreshTokenDuration)
+	assert.Equal(t, 30, cfg.Probod.Auth.OAuth2Server.AuthorizationCodeDuration)
+	assert.Equal(t, 40, cfg.Probod.Auth.OAuth2Server.DeviceCodeDuration)
+}
+
+func TestBuilder_Build_OAuth2Preset(t *testing.T) {
+	env := requiredEnv()
+	delete(env, "OAUTH2_SERVER_SIGNING_KEY")
+
+	b := NewBuilder(mockEnv(env))
+	b.oauth2SigningKey = "preset-signing-key"
+
+	cfg, err := b.Build()
+	require.NoError(t, err)
+
+	require.Len(t, cfg.Probod.Auth.OAuth2Server.SigningKeys, 1)
+	assert.Equal(t, "preset-signing-key", cfg.Probod.Auth.OAuth2Server.SigningKeys[0].PrivateKey)
+}
+
 func TestBuilder_Build_PgCABundleFromEnv(t *testing.T) {
 	env := requiredEnv()
 	env["PG_CA_BUNDLE"] = "test-ca-bundle-content"

pkg/bootstrap/oauth2.go

@@ -0,0 +1,41 @@
+// Copyright (c) 2026 Probo Inc <hello@getprobo.com>.
+//
+// Permission to use, copy, modify, and/or distribute this software for any
+// purpose with or without fee is hereby granted, provided that the above
+// copyright notice and this permission notice appear in all copies.
+//
+// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
+// REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
+// AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
+// INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
+// LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
+// OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
+// PERFORMANCE OF THIS SOFTWARE.
+
+package bootstrap
+
+import (
+	"crypto/rand"
+	"crypto/rsa"
+	"crypto/x509"
+	"encoding/pem"
+	"fmt"
+)
+
+const oauth2SigningKeyBits = 2048
+
+// GenerateOAuth2SigningKey returns a freshly generated 2048-bit RSA
+// private key PKCS#1-encoded as PEM.
+func GenerateOAuth2SigningKey() (string, error) {
+	privateKey, err := rsa.GenerateKey(rand.Reader, oauth2SigningKeyBits)
+	if err != nil {
+		return "", fmt.Errorf("generate RSA key: %w", err)
+	}
+
+	keyPEM := pem.EncodeToMemory(&pem.Block{
+		Type:  "RSA PRIVATE KEY",
+		Bytes: x509.MarshalPKCS1PrivateKey(privateKey),
+	})
+
+	return string(keyPEM), nil
+}

pkg/bootstrap/oauth2_test.go

@@ -0,0 +1,52 @@
+// Copyright (c) 2026 Probo Inc <hello@getprobo.com>.
+//
+// Permission to use, copy, modify, and/or distribute this software for any
+// purpose with or without fee is hereby granted, provided that the above
+// copyright notice and this permission notice appear in all copies.
+//
+// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
+// REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
+// AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
+// INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
+// LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
+// OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
+// PERFORMANCE OF THIS SOFTWARE.
+
+package bootstrap
+
+import (
+	"crypto/x509"
+	"encoding/pem"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestGenerateOAuth2SigningKey(t *testing.T) {
+	t.Parallel()
+
+	key, err := GenerateOAuth2SigningKey()
+	require.NoError(t, err)
+
+	block, _ := pem.Decode([]byte(key))
+	require.NotNil(t, block, "private key should be valid PEM")
+	assert.Equal(t, "RSA PRIVATE KEY", block.Type)
+
+	parsed, err := x509.ParsePKCS1PrivateKey(block.Bytes)
+	require.NoError(t, err)
+
+	assert.Equal(t, oauth2SigningKeyBits, parsed.N.BitLen())
+}
+
+func TestGenerateOAuth2SigningKey_Unique(t *testing.T) {
+	t.Parallel()
+
+	key1, err := GenerateOAuth2SigningKey()
+	require.NoError(t, err)
+
+	key2, err := GenerateOAuth2SigningKey()
+	require.NoError(t, err)
+
+	assert.NotEqual(t, key1, key2)
+}

pkg/probod/auth_config.go

@@ -41,9 +41,9 @@ type OAuth2ServerConfig struct {
 }
 
 type OAuth2SigningKeyConfig struct {
-	KeyFile string `json:"key-file"`
+	PrivateKey string `json:"private-key"`
-	KID     string `json:"kid"`
+	KID        string `json:"kid"`
-	Active  bool   `json:"active"`
+	Active     bool   `json:"active"`
 }
 
 type CookieConfig struct {

pkg/probod/probod.go

@@ -25,7 +25,6 @@ import (
 	"fmt"
 	"net"
 	"net/http"
-	"os"
 	"strings"
 	"sync"
 	"time"
@@ -389,12 +388,7 @@ func (impl *Implm) Run(
 	var oauth2SigningKeys oauth2server.SigningKeys
 	var hasActive bool
 	for _, keyCfg := range impl.cfg.Auth.OAuth2Server.SigningKeys {
-		keyPEM, err := os.ReadFile(keyCfg.KeyFile)
+		signer, err := pemutil.DecodePrivateKey([]byte(keyCfg.PrivateKey))
-		if err != nil {
-			return fmt.Errorf("cannot read OAuth2 server signing key file: %w", err)
-		}
-
-		signer, err := pemutil.DecodePrivateKey(keyPEM)
 		if err != nil {
 			return fmt.Errorf("cannot decode OAuth2 server signing key: %w", err)
 		}