From db7f4438b4ad189390c996a1918549da461200b7 Mon Sep 17 00:00:00 2001
From: Yevhenii Shcherbina <evgeniy.shcherbina.es@gmail.com>
Date: Wed, 1 Jul 2026 16:44:15 -0400
Subject: [PATCH] feat: generate STS external ID for Bedrock role assumption
 (#26869)

Implements:
https://linear.app/codercom/issue/AIGOV-495/add-externalid-to-prevent-confused-deputy-problem

When a Bedrock provider assumes an IAM role via STS, the gateway now
generates a unique external ID for it and sends that value on every
`AssumeRole` call. The external ID guards against the [confused deputy
problem](https://docs.aws.amazon.com/IAM/latest/UserGuide/confused-deputy.html)
on cross-account role assumption. Per [AWS's
recommendation](https://docs.aws.amazon.com/IAM/latest/UserGuide/id_roles_create_for-user_externalid.html),
the gateway generates and owns the value rather than accepting one from
the operator; that ownership is what makes it effective, since a party
who knows another's external ID can't induce the gateway to send it.

The external ID is server-owned and read-only over the API. It is
generated once, when a provider first has a `role_arn`, and is stable
thereafter. Clients cannot set it: create rejects any supplied
`external_id`, and update rejects a value that differs from the stored
one. An update may echo the stored value back unchanged, so the normal
read-modify-write flow (GET the provider, change a field, PATCH the full
settings object) keeps working. The value is not a secret and is
returned on GET so operators can copy it into the target role's trust
policy as an `sts:ExternalId` condition.

It is persisted in the existing JSON settings blob, so there is no
migration or audit-table change.
---
 aibridge/config/config.go                  |   4 +
 aibridge/provider/bedrock.go               |   3 +
 aibridge/provider/bedrock_internal_test.go |  55 +++++
 cli/aibridged.go                           |   2 +
 coderd/ai_providers.go                     |  55 +++++
 coderd/ai_providers_internal_test.go       |  89 ++++++++
 coderd/ai_providers_test.go                | 223 +++++++++++++++++++++
 coderd/aibridged/proto/aibridged.pb.go     | 142 +++++++------
 coderd/aibridged/proto/aibridged.proto     |   1 +
 coderd/aibridgedserver/aibridgedserver.go  |   1 +
 codersdk/aiproviders.go                    |   6 +
 codersdk/aiproviders_bedrock.go            |   5 +
 site/src/api/typesGenerated.ts             |   7 +
 13 files changed, 527 insertions(+), 66 deletions(-)
 create mode 100644 coderd/ai_providers_internal_test.go

diff --git a/aibridge/config/config.go b/aibridge/config/config.go
index 3dc76841aa..b01282b0cc 100644
--- a/aibridge/config/config.go
+++ b/aibridge/config/config.go
@@ -38,6 +38,10 @@ type AWSBedrock struct {
 	// IRSA / EKS Pod Identity / EC2 Instance Profile) signs the AssumeRole
 	// call, and the resulting temporary credentials sign Bedrock requests.
 	RoleARN string
+	// ExternalID is sent as the STS external ID on the AssumeRole call.
+	// It is meaningful only alongside RoleARN and must match the
+	// sts:ExternalId condition on the target role's trust policy.
+	ExternalID string
 }
 
 // OpenAI carries configuration for an OpenAI provider.
diff --git a/aibridge/provider/bedrock.go b/aibridge/provider/bedrock.go
index 93bbf7038a..013430f1d7 100644
--- a/aibridge/provider/bedrock.go
+++ b/aibridge/provider/bedrock.go
@@ -79,6 +79,9 @@ func buildBedrockCredentials(ctx context.Context, cfg config.AWSBedrock) (aws.Cr
 	if cfg.RoleARN != "" {
 		credsProvider = stscreds.NewAssumeRoleProvider(sts.NewFromConfig(base), cfg.RoleARN, func(o *stscreds.AssumeRoleOptions) {
 			o.RoleSessionName = bedrockSessionName
+			if cfg.ExternalID != "" {
+				o.ExternalID = aws.String(cfg.ExternalID)
+			}
 		})
 		credsProvider = aws.NewCredentialsCache(credsProvider)
 	}
diff --git a/aibridge/provider/bedrock_internal_test.go b/aibridge/provider/bedrock_internal_test.go
index 0ecae6c780..1cb7764c89 100644
--- a/aibridge/provider/bedrock_internal_test.go
+++ b/aibridge/provider/bedrock_internal_test.go
@@ -207,6 +207,61 @@ func TestBuildBedrockCredentialsAssumeRole(t *testing.T) {
 	require.Equal(t, bedrockSessionName, gotSessionName)
 }
 
+// TestBuildBedrockCredentialsAssumeRoleExternalID verifies that a configured
+// external ID is sent on the STS AssumeRole call, and that omitting it sends
+// no ExternalId parameter.
+// NOTE: no t.Parallel() because it uses t.Setenv.
+func TestBuildBedrockCredentialsAssumeRoleExternalID(t *testing.T) {
+	tests := []struct {
+		name           string
+		externalID     string
+		wantExternalID string
+	}{
+		{name: "with external id", externalID: "trust-policy-id-123", wantExternalID: "trust-policy-id-123"},
+		{name: "without external id", externalID: "", wantExternalID: ""},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			var gotExternalID string
+			// Mock the AWS STS AssumeRole API.
+			// https://docs.aws.amazon.com/STS/latest/APIReference/API_AssumeRole.html
+			sts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+				require.NoError(t, r.ParseForm())
+				gotExternalID = r.Form.Get("ExternalId")
+
+				w.Header().Set("Content-Type", "text/xml")
+				_, _ = w.Write([]byte(`<AssumeRoleResponse xmlns="https://sts.amazonaws.com/doc/2011-06-15/">
+  <AssumeRoleResult>
+    <Credentials>
+      <AccessKeyId>ASIAASSUMED</AccessKeyId>
+      <SecretAccessKey>assumed-secret</SecretAccessKey>
+      <SessionToken>assumed-token</SessionToken>
+      <Expiration>2999-01-01T00:00:00Z</Expiration>
+    </Credentials>
+  </AssumeRoleResult>
+</AssumeRoleResponse>`))
+			}))
+			defer sts.Close()
+
+			t.Setenv("AWS_ENDPOINT_URL_STS", sts.URL)
+			t.Setenv("AWS_ACCESS_KEY_ID", "base-key")
+			t.Setenv("AWS_SECRET_ACCESS_KEY", "base-secret")
+
+			creds, _, err := buildBedrockCredentials(context.Background(), config.AWSBedrock{
+				Region:     "us-east-1",
+				RoleARN:    "arn:aws:iam::123456789012:role/target",
+				ExternalID: tt.externalID,
+			})
+			require.NoError(t, err)
+
+			_, err = creds.Retrieve(context.Background())
+			require.NoError(t, err)
+			require.Equal(t, tt.wantExternalID, gotExternalID)
+		})
+	}
+}
+
 // TestBuildBedrockCredentialsAssumeRoleError verifies that when STS rejects the
 // AssumeRole call (e.g. a trust-policy or IAM denial), the failure surfaces to
 // the caller on Retrieve with enough detail to diagnose it, rather than being
diff --git a/cli/aibridged.go b/cli/aibridged.go
index 87e583b573..addeb3f959 100644
--- a/cli/aibridged.go
+++ b/cli/aibridged.go
@@ -211,6 +211,7 @@ func protoToProviderSpec(pp *proto.AIProvider) aiProviderSpec {
 			b.GetSmallFastModel(),
 		)
 		bedrock.RoleARN = b.GetRoleArn()
+		bedrock.ExternalID = b.GetExternalId()
 		spec.Bedrock = ptr.Ref(bedrock)
 	}
 	return spec
@@ -352,6 +353,7 @@ func bedrockConfig(baseURL string, bedrock *codersdk.AIProviderBedrockSettings)
 		Model:           bedrockSettings.Model,
 		SmallFastModel:  bedrockSettings.SmallFastModel,
 		RoleARN:         bedrockSettings.RoleARN,
+		ExternalID:      bedrockSettings.ExternalID,
 	}
 }
 
diff --git a/coderd/ai_providers.go b/coderd/ai_providers.go
index 49e5bb8750..a00e026800 100644
--- a/coderd/ai_providers.go
+++ b/coderd/ai_providers.go
@@ -2,6 +2,7 @@ package coderd
 
 import (
 	"context"
+	"crypto/rand"
 	"database/sql"
 	"encoding/json"
 	"errors"
@@ -178,6 +179,9 @@ func (api *API) aiProvidersCreate(rw http.ResponseWriter, r *http.Request) {
 		return
 	}
 
+	// Generate the server-owned external ID when the provider assumes a role.
+	ensureBedrockExternalID(&req.Settings)
+
 	settings, err := encodeAIProviderSettings(req.Settings)
 	if err != nil {
 		api.Logger.Error(ctx, "encode AI provider settings", slog.Error(err))
@@ -318,6 +322,9 @@ func (api *API) aiProvidersUpdate(rw http.ResponseWriter, r *http.Request) {
 			return xerrors.Errorf("decode existing settings: %w", err)
 		}
 		if req.Settings != nil {
+			if err := validateBedrockExternalIDUnchanged(existing, *req.Settings); err != nil {
+				return err
+			}
 			existing = mergeAIProviderSettings(existing, *req.Settings)
 		}
 		// Bedrock settings are only meaningful for anthropic- or
@@ -329,6 +336,9 @@ func (api *API) aiProvidersUpdate(rw http.ResponseWriter, r *http.Request) {
 			old.Type != database.AIProviderTypeBedrock {
 			return errAIProviderBedrockTypeMismatch
 		}
+		// Generate the server-owned external ID when the provider assumes a role
+		// and lacks one.
+		ensureBedrockExternalID(&existing)
 		settings, err := encodeAIProviderSettings(existing)
 		if err != nil {
 			return xerrors.Errorf("encode settings: %w", err)
@@ -400,6 +410,12 @@ func (api *API) aiProvidersUpdate(rw http.ResponseWriter, r *http.Request) {
 		})
 		return
 	}
+	if errors.Is(err, errAIProviderExternalIDReadOnly) {
+		httpapi.Write(ctx, rw, http.StatusBadRequest, codersdk.Response{
+			Message: "The Bedrock external ID is server-generated and cannot be changed.",
+		})
+		return
+	}
 	if errors.Is(err, errAIProviderKeyUnknown) {
 		// Use the sentinel directly so the response message does not
 		// leak the "execute transaction:" wrapper xerrors added on the
@@ -506,6 +522,12 @@ var errCopilotRejectsAPIKeys = xerrors.New("copilot providers do not accept api_
 // the outer handler translates it into a 400.
 var errAIProviderBedrockTypeMismatch = xerrors.New("bedrock settings are only valid for type=anthropic or type=bedrock")
 
+// errAIProviderExternalIDReadOnly is the sentinel returned from inside
+// the update transaction when a patch tries to change the server-owned
+// Bedrock external ID; the outer handler translates it into a 400. A
+// patch may echo the stored value but not set a different one.
+var errAIProviderExternalIDReadOnly = xerrors.New("external_id is server-generated and cannot be changed")
+
 // errAIProviderInvalidName is returned from lookupAIProvider when the
 // idOrName parameter is neither a UUID nor a syntactically-valid name.
 // The handler translates this into a 400 so an integrator gets a hint
@@ -772,6 +794,39 @@ func mergeAIProviderSettings(existing, patch codersdk.AIProviderSettings) coders
 		if merged.AccessKeySecret == nil {
 			merged.AccessKeySecret = existing.Bedrock.AccessKeySecret
 		}
+		// The external ID is server-owned and stable: carry the stored value
+		// forward so a patch can't change it. A patch that sets a different
+		// value is rejected upstream.
+		merged.ExternalID = existing.Bedrock.ExternalID
 	}
 	return codersdk.AIProviderSettings{Bedrock: &merged}
 }
+
+// validateBedrockExternalIDUnchanged rejects a patch that sets a Bedrock
+// external ID different from the stored one. A patch may echo the stored
+// value (read-modify-write resends it) but not change it; the value is
+// server-owned.
+func validateBedrockExternalIDUnchanged(existing, patch codersdk.AIProviderSettings) error {
+	stored := ""
+	if existing.Bedrock != nil {
+		stored = existing.Bedrock.ExternalID
+	}
+
+	provided := ""
+	if patch.Bedrock != nil {
+		provided = patch.Bedrock.ExternalID
+	}
+
+	if provided != "" && provided != stored {
+		return errAIProviderExternalIDReadOnly
+	}
+	return nil
+}
+
+// ensureBedrockExternalID assigns a server-owned STS external ID when the
+// Bedrock provider assumes a role and none is set yet.
+func ensureBedrockExternalID(s *codersdk.AIProviderSettings) {
+	if s.Bedrock != nil && s.Bedrock.RoleARN != "" && s.Bedrock.ExternalID == "" {
+		s.Bedrock.ExternalID = rand.Text()
+	}
+}
diff --git a/coderd/ai_providers_internal_test.go b/coderd/ai_providers_internal_test.go
new file mode 100644
index 0000000000..102dd9ac45
--- /dev/null
+++ b/coderd/ai_providers_internal_test.go
@@ -0,0 +1,89 @@
+package coderd
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+
+	"github.com/coder/coder/v2/codersdk"
+)
+
+// TestEnsureBedrockExternalID covers the server-owned external ID generation:
+// it generates only when a role is configured and none is set, and never
+// overwrites an existing value.
+func TestEnsureBedrockExternalID(t *testing.T) {
+	t.Parallel()
+
+	t.Run("NilBedrockIsNoOp", func(t *testing.T) {
+		t.Parallel()
+		s := codersdk.AIProviderSettings{}
+		ensureBedrockExternalID(&s)
+		require.Nil(t, s.Bedrock)
+	})
+
+	t.Run("NoRoleLeavesEmpty", func(t *testing.T) {
+		t.Parallel()
+		s := codersdk.AIProviderSettings{Bedrock: &codersdk.AIProviderBedrockSettings{Region: "us-east-1"}}
+		ensureBedrockExternalID(&s)
+		require.Empty(t, s.Bedrock.ExternalID)
+	})
+
+	t.Run("GeneratesWhenRoleSet", func(t *testing.T) {
+		t.Parallel()
+		s := codersdk.AIProviderSettings{Bedrock: &codersdk.AIProviderBedrockSettings{
+			RoleARN: "arn:aws:iam::123456789012:role/BedrockRole",
+		}}
+		ensureBedrockExternalID(&s)
+		// The bounds are a sanity floor and ceiling, not a correctness
+		// requirement. crypto/rand.Text() currently returns 26 chars, but
+		// its docs allow future Go versions to return longer text. If a Go
+		// upgrade trips these bounds, widen them or use different function.
+		require.GreaterOrEqual(t, len(s.Bedrock.ExternalID), 26)
+		require.LessOrEqual(t, len(s.Bedrock.ExternalID), 52)
+	})
+
+	t.Run("DoesNotOverwriteExisting", func(t *testing.T) {
+		t.Parallel()
+		s := codersdk.AIProviderSettings{Bedrock: &codersdk.AIProviderBedrockSettings{
+			RoleARN:    "arn:aws:iam::123456789012:role/BedrockRole",
+			ExternalID: "existing-value",
+		}}
+		ensureBedrockExternalID(&s)
+		require.Equal(t, "existing-value", s.Bedrock.ExternalID)
+	})
+
+	t.Run("GeneratesUniqueValues", func(t *testing.T) {
+		t.Parallel()
+		seen := make(map[string]struct{})
+		for range 10 {
+			s := codersdk.AIProviderSettings{Bedrock: &codersdk.AIProviderBedrockSettings{
+				RoleARN: "arn:aws:iam::123456789012:role/BedrockRole",
+			}}
+			ensureBedrockExternalID(&s)
+			_, dup := seen[s.Bedrock.ExternalID]
+			require.False(t, dup, "external IDs must be unique per provider")
+			seen[s.Bedrock.ExternalID] = struct{}{}
+		}
+	})
+}
+
+// TestMergeAIProviderSettingsExternalID verifies the external ID is treated as
+// server-owned during a PATCH merge: a stored value is carried forward and
+// overrides the patch so it can't be changed.
+func TestMergeAIProviderSettingsExternalID(t *testing.T) {
+	t.Parallel()
+
+	roleARN := "arn:aws:iam::123456789012:role/BedrockRole"
+	existing := codersdk.AIProviderSettings{Bedrock: &codersdk.AIProviderBedrockSettings{
+		RoleARN:    roleARN,
+		ExternalID: "stored-value",
+	}}
+	patch := codersdk.AIProviderSettings{Bedrock: &codersdk.AIProviderBedrockSettings{
+		RoleARN:    roleARN,
+		ExternalID: "client-supplied-value",
+	}}
+	merged := mergeAIProviderSettings(existing, patch)
+	require.NotNil(t, merged.Bedrock)
+	require.Equal(t, roleARN, merged.Bedrock.RoleARN)
+	require.Equal(t, "stored-value", merged.Bedrock.ExternalID)
+}
diff --git a/coderd/ai_providers_test.go b/coderd/ai_providers_test.go
index 4fcc1dd63b..32e6b8947d 100644
--- a/coderd/ai_providers_test.go
+++ b/coderd/ai_providers_test.go
@@ -1554,3 +1554,226 @@ func TestAIProviderSettingsMerge(t *testing.T) {
 		require.Equal(t, "", *persisted.Bedrock.AccessKeySecret)
 	})
 }
+
+// TestAIProvidersBedrockExternalID covers the server-owned STS external ID:
+// it is generated when (and only when) the provider assumes a role, is
+// rejected when a client tries to set or change it, and is stable across
+// PATCHes that echo the stored value.
+func TestAIProvidersBedrockExternalID(t *testing.T) {
+	t.Parallel()
+
+	const (
+		roleARN               = "arn:aws:iam::123456789012:role/BedrockRole"
+		externalIDReadOnlyMsg = "The Bedrock external ID is server-generated and cannot be changed."
+	)
+
+	createBedrock := func(t *testing.T, client *codersdk.Client, name string, b codersdk.AIProviderBedrockSettings) (codersdk.AIProvider, error) {
+		t.Helper()
+		ctx := testutil.Context(t, testutil.WaitLong)
+		//nolint:gocritic // Owner role is the audience for this endpoint.
+		return client.CreateAIProvider(ctx, codersdk.CreateAIProviderRequest{
+			Type:     codersdk.AIProviderTypeBedrock,
+			Name:     name,
+			Enabled:  true,
+			BaseURL:  "https://bedrock-runtime.us-east-1.amazonaws.com",
+			Settings: codersdk.AIProviderSettings{Bedrock: &b},
+		})
+	}
+
+	t.Run("GeneratedWhenRoleSet", func(t *testing.T) {
+		t.Parallel()
+		client := coderdtest.New(t, nil)
+		_ = coderdtest.CreateFirstUser(t, client)
+		ctx := testutil.Context(t, testutil.WaitLong)
+
+		created, err := createBedrock(t, client, "bedrock-role", codersdk.AIProviderBedrockSettings{
+			Region:  "us-east-1",
+			RoleARN: roleARN,
+		})
+		require.NoError(t, err)
+		require.NotNil(t, created.Settings.Bedrock)
+		require.NotEmpty(t, created.Settings.Bedrock.ExternalID, "external ID must be generated when a role is set")
+
+		// GET returns the same external ID.
+		got, err := client.AIProvider(ctx, created.ID.String())
+		require.NoError(t, err)
+		require.Equal(t, created.Settings.Bedrock.ExternalID, got.Settings.Bedrock.ExternalID)
+	})
+
+	t.Run("AbsentWithoutRole", func(t *testing.T) {
+		t.Parallel()
+		client := coderdtest.New(t, nil)
+		_ = coderdtest.CreateFirstUser(t, client)
+
+		created, err := createBedrock(t, client, "bedrock-no-role", codersdk.AIProviderBedrockSettings{Region: "us-east-1"})
+		require.NoError(t, err)
+		require.NotNil(t, created.Settings.Bedrock)
+		require.Empty(t, created.Settings.Bedrock.ExternalID, "no external ID without a role to assume")
+	})
+
+	t.Run("RejectsClientValueOnCreate", func(t *testing.T) {
+		t.Parallel()
+		client := coderdtest.New(t, nil)
+		_ = coderdtest.CreateFirstUser(t, client)
+
+		_, err := createBedrock(t, client, "bedrock-client-id", codersdk.AIProviderBedrockSettings{
+			Region:     "us-east-1",
+			RoleARN:    roleARN,
+			ExternalID: "client-supplied-value",
+		})
+		sdkErr := requireSDKError(t, err, http.StatusBadRequest)
+		require.Contains(t, sdkErr.Validations, codersdk.ValidationError{
+			Field:  "settings.external_id",
+			Detail: "external_id is server-generated and cannot be set",
+		})
+	})
+
+	t.Run("StableWhenPatchOmitsValue", func(t *testing.T) {
+		t.Parallel()
+		client := coderdtest.New(t, nil)
+		_ = coderdtest.CreateFirstUser(t, client)
+		ctx := testutil.Context(t, testutil.WaitLong)
+
+		created, err := createBedrock(t, client, "bedrock-stable", codersdk.AIProviderBedrockSettings{
+			Region:  "us-east-1",
+			RoleARN: roleARN,
+		})
+		require.NoError(t, err)
+		original := created.Settings.Bedrock.ExternalID
+		require.NotEmpty(t, original)
+
+		updated, err := client.UpdateAIProvider(ctx, created.Name, codersdk.UpdateAIProviderRequest{
+			Settings: &codersdk.AIProviderSettings{
+				Bedrock: &codersdk.AIProviderBedrockSettings{Region: "us-west-2", RoleARN: roleARN},
+			},
+		})
+		require.NoError(t, err)
+		require.Equal(t, "us-west-2", updated.Settings.Bedrock.Region)
+		require.Equal(t, original, updated.Settings.Bedrock.ExternalID, "external ID must be stable across PATCH")
+	})
+
+	t.Run("StableAcrossRoleRemovalAndReassignment", func(t *testing.T) {
+		t.Parallel()
+		client := coderdtest.New(t, nil)
+		_ = coderdtest.CreateFirstUser(t, client)
+		ctx := testutil.Context(t, testutil.WaitLong)
+
+		const roleB = "arn:aws:iam::123456789012:role/BedrockRoleB"
+
+		created, err := createBedrock(t, client, "bedrock-toggle", codersdk.AIProviderBedrockSettings{
+			Region:  "us-east-1",
+			RoleARN: roleARN,
+		})
+		require.NoError(t, err)
+		original := created.Settings.Bedrock.ExternalID
+		require.NotEmpty(t, original)
+
+		// Removing the role retains the external ID.
+		cleared, err := client.UpdateAIProvider(ctx, created.Name, codersdk.UpdateAIProviderRequest{
+			Settings: &codersdk.AIProviderSettings{
+				Bedrock: &codersdk.AIProviderBedrockSettings{Region: "us-east-1"},
+			},
+		})
+		require.NoError(t, err)
+		require.Empty(t, cleared.Settings.Bedrock.RoleARN)
+		require.Equal(t, original, cleared.Settings.Bedrock.ExternalID)
+
+		// Adding a different role reuses the retained ID rather than
+		// regenerating it, so a trust policy referencing it keeps working.
+		readded, err := client.UpdateAIProvider(ctx, created.Name, codersdk.UpdateAIProviderRequest{
+			Settings: &codersdk.AIProviderSettings{
+				Bedrock: &codersdk.AIProviderBedrockSettings{Region: "us-east-1", RoleARN: roleB},
+			},
+		})
+		require.NoError(t, err)
+		require.Equal(t, roleB, readded.Settings.Bedrock.RoleARN)
+		require.Equal(t, original, readded.Settings.Bedrock.ExternalID, "external ID must survive role removal and re-add")
+	})
+
+	t.Run("AllowsEchoedValueOnPatch", func(t *testing.T) {
+		t.Parallel()
+		client := coderdtest.New(t, nil)
+		_ = coderdtest.CreateFirstUser(t, client)
+		ctx := testutil.Context(t, testutil.WaitLong)
+
+		created, err := createBedrock(t, client, "bedrock-echo", codersdk.AIProviderBedrockSettings{
+			Region:  "us-east-1",
+			RoleARN: roleARN,
+		})
+		require.NoError(t, err)
+		original := created.Settings.Bedrock.ExternalID
+		require.NotEmpty(t, original)
+
+		// Read-modify-write resends the whole settings, including the stored
+		// external ID. Echoing the same value is allowed.
+		updated, err := client.UpdateAIProvider(ctx, created.Name, codersdk.UpdateAIProviderRequest{
+			Settings: &codersdk.AIProviderSettings{
+				Bedrock: &codersdk.AIProviderBedrockSettings{Region: "us-west-2", RoleARN: roleARN, ExternalID: original},
+			},
+		})
+		require.NoError(t, err)
+		require.Equal(t, "us-west-2", updated.Settings.Bedrock.Region)
+		require.Equal(t, original, updated.Settings.Bedrock.ExternalID)
+	})
+
+	t.Run("RejectsChangedValueOnPatch", func(t *testing.T) {
+		t.Parallel()
+		client := coderdtest.New(t, nil)
+		_ = coderdtest.CreateFirstUser(t, client)
+		ctx := testutil.Context(t, testutil.WaitLong)
+
+		created, err := createBedrock(t, client, "bedrock-change", codersdk.AIProviderBedrockSettings{
+			Region:  "us-east-1",
+			RoleARN: roleARN,
+		})
+		require.NoError(t, err)
+		require.NotEmpty(t, created.Settings.Bedrock.ExternalID)
+
+		_, err = client.UpdateAIProvider(ctx, created.Name, codersdk.UpdateAIProviderRequest{
+			Settings: &codersdk.AIProviderSettings{
+				Bedrock: &codersdk.AIProviderBedrockSettings{Region: "us-east-1", RoleARN: roleARN, ExternalID: "client-tries-to-change-it"},
+			},
+		})
+		sdkErr := requireSDKError(t, err, http.StatusBadRequest)
+		require.Equal(t, externalIDReadOnlyMsg, sdkErr.Message)
+	})
+
+	t.Run("GeneratedWhenRoleAddedByPatch", func(t *testing.T) {
+		t.Parallel()
+		client := coderdtest.New(t, nil)
+		_ = coderdtest.CreateFirstUser(t, client)
+		ctx := testutil.Context(t, testutil.WaitLong)
+
+		created, err := createBedrock(t, client, "bedrock-add-role", codersdk.AIProviderBedrockSettings{Region: "us-east-1"})
+		require.NoError(t, err)
+		require.Empty(t, created.Settings.Bedrock.ExternalID)
+
+		updated, err := client.UpdateAIProvider(ctx, created.Name, codersdk.UpdateAIProviderRequest{
+			Settings: &codersdk.AIProviderSettings{
+				Bedrock: &codersdk.AIProviderBedrockSettings{Region: "us-east-1", RoleARN: roleARN},
+			},
+		})
+		require.NoError(t, err)
+		require.NotEmpty(t, updated.Settings.Bedrock.ExternalID, "external ID must be generated when a role is added by PATCH")
+	})
+
+	t.Run("RejectsClientValueWhenRoleAddedByPatch", func(t *testing.T) {
+		t.Parallel()
+		client := coderdtest.New(t, nil)
+		_ = coderdtest.CreateFirstUser(t, client)
+		ctx := testutil.Context(t, testutil.WaitLong)
+
+		created, err := createBedrock(t, client, "bedrock-add-role-id", codersdk.AIProviderBedrockSettings{Region: "us-east-1"})
+		require.NoError(t, err)
+		require.Empty(t, created.Settings.Bedrock.ExternalID)
+
+		// No value is stored yet, so any client value is a change and is rejected.
+		_, err = client.UpdateAIProvider(ctx, created.Name, codersdk.UpdateAIProviderRequest{
+			Settings: &codersdk.AIProviderSettings{
+				Bedrock: &codersdk.AIProviderBedrockSettings{Region: "us-east-1", RoleARN: roleARN, ExternalID: "client-supplied-value"},
+			},
+		})
+		sdkErr := requireSDKError(t, err, http.StatusBadRequest)
+		require.Equal(t, externalIDReadOnlyMsg, sdkErr.Message)
+	})
+}
diff --git a/coderd/aibridged/proto/aibridged.pb.go b/coderd/aibridged/proto/aibridged.pb.go
index f503aaa8fb..b4be124d97 100644
--- a/coderd/aibridged/proto/aibridged.pb.go
+++ b/coderd/aibridged/proto/aibridged.pb.go
@@ -1454,6 +1454,7 @@ type AIProviderKindBedrock struct {
 	Model           string `protobuf:"bytes,4,opt,name=model,proto3" json:"model,omitempty"`
 	SmallFastModel  string `protobuf:"bytes,5,opt,name=small_fast_model,json=smallFastModel,proto3" json:"small_fast_model,omitempty"`
 	RoleArn         string `protobuf:"bytes,6,opt,name=role_arn,json=roleArn,proto3" json:"role_arn,omitempty"`
+	ExternalId      string `protobuf:"bytes,7,opt,name=external_id,json=externalId,proto3" json:"external_id,omitempty"`
 }
 
 func (x *AIProviderKindBedrock) Reset() {
@@ -1530,6 +1531,13 @@ func (x *AIProviderKindBedrock) GetRoleArn() string {
 	return ""
 }
 
+func (x *AIProviderKindBedrock) GetExternalId() string {
+	if x != nil {
+		return x.ExternalId
+	}
+	return ""
+}
+
 var File_coderd_aibridged_proto_aibridged_proto protoreflect.FileDescriptor
 
 var file_coderd_aibridged_proto_aibridged_proto_rawDesc = []byte{
@@ -1802,7 +1810,7 @@ var file_coderd_aibridged_proto_aibridged_proto_rawDesc = []byte{
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@@ -1816,72 +1824,74 @@ var file_coderd_aibridged_proto_aibridged_proto_rawDesc = []byte{
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 }
 
 var (
diff --git a/coderd/aibridged/proto/aibridged.proto b/coderd/aibridged/proto/aibridged.proto
index 1d22ccdaa8..8dc78e7a89 100644
--- a/coderd/aibridged/proto/aibridged.proto
+++ b/coderd/aibridged/proto/aibridged.proto
@@ -193,4 +193,5 @@ message AIProviderKindBedrock {
   string model = 4;
   string small_fast_model = 5;
   string role_arn = 6;
+  string external_id = 7;
 }
diff --git a/coderd/aibridgedserver/aibridgedserver.go b/coderd/aibridgedserver/aibridgedserver.go
index 78f11cd9cc..8b539153e9 100644
--- a/coderd/aibridgedserver/aibridgedserver.go
+++ b/coderd/aibridgedserver/aibridgedserver.go
@@ -883,6 +883,7 @@ func aiProviderToProto(row database.AIProvider, keys []database.AIProviderKey) (
 			Model:           settings.Bedrock.Model,
 			SmallFastModel:  settings.Bedrock.SmallFastModel,
 			RoleArn:         settings.Bedrock.RoleARN,
+			ExternalId:      settings.Bedrock.ExternalID,
 		}
 	}
 
diff --git a/codersdk/aiproviders.go b/codersdk/aiproviders.go
index 5632ff5684..7826a921f2 100644
--- a/codersdk/aiproviders.go
+++ b/codersdk/aiproviders.go
@@ -275,6 +275,12 @@ func (req CreateAIProviderRequest) Validate() []ValidationError {
 	}
 	if req.Settings.Bedrock != nil {
 		validations = append(validations, validateAIProviderRoleARN(req.Settings.Bedrock.RoleARN)...)
+		if req.Settings.Bedrock.ExternalID != "" {
+			validations = append(validations, ValidationError{
+				Field:  "settings.external_id",
+				Detail: "external_id is server-generated and cannot be set",
+			})
+		}
 	}
 	if req.Type == AIProviderTypeCopilot && len(req.APIKeys) > 0 {
 		validations = append(validations, ValidationError{
diff --git a/codersdk/aiproviders_bedrock.go b/codersdk/aiproviders_bedrock.go
index 360b763333..be17f6c95d 100644
--- a/codersdk/aiproviders_bedrock.go
+++ b/codersdk/aiproviders_bedrock.go
@@ -35,6 +35,11 @@ type AIProviderBedrockSettings struct {
 	// IRSA / EKS Pod Identity / EC2 Instance Profile) signs the AssumeRole
 	// call, and the resulting temporary credentials sign Bedrock requests.
 	RoleARN string `json:"role_arn,omitempty"`
+	// ExternalID is the STS external ID sent on the AssumeRole call when
+	// RoleARN is set. The server generates and owns it: create and update
+	// reject any client-supplied value that differs from the stored one (an
+	// update may echo the stored value back).
+	ExternalID string `json:"external_id,omitempty"`
 }
 
 // IsConfigured reports whether any load-bearing Bedrock field is set,
diff --git a/site/src/api/typesGenerated.ts b/site/src/api/typesGenerated.ts
index b7723777f1..09e6ac16cb 100644
--- a/site/src/api/typesGenerated.ts
+++ b/site/src/api/typesGenerated.ts
@@ -335,6 +335,13 @@ export interface AIProviderBedrockSettings {
 	 * call, and the resulting temporary credentials sign Bedrock requests.
 	 */
 	readonly role_arn?: string;
+	/**
+	 * ExternalID is the STS external ID sent on the AssumeRole call when
+	 * RoleARN is set. The server generates and owns it: create and update
+	 * reject any client-supplied value that differs from the stored one (an
+	 * update may echo the stored value back).
+	 */
+	readonly external_id?: string;
 }
 
 // From codersdk/aiproviders_bedrock.go