Add Anthropic access-review driver and resolver

The driver lists organization members through the Anthropic Admin API
(GET /v1/organizations/users) with cursor pagination, mapping the role
and the RFC 3339 added_at timestamp. The name resolver reads the
organization name from /v1/organizations/me; a non-2xx response (for
example a revoked key) yields no name rather than making the
source-name worker retry forever. Both send the required
anthropic-version header.

Add a VCR test helper that injects the key via x-api-key so the
cassette stays recordable, and strip x-api-key on save. The cassette
holds synthetic members covering the user, developer, and admin roles.

Signed-off-by: Aurélien Sibiril <81782+aureliensibiril@users.noreply.github.com>

pkg/accessreview/drivers/anthropic.go

@@ -0,0 +1,159 @@
+// 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 drivers
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"net/http"
+	"time"
+
+	"go.probo.inc/probo/pkg/coredata"
+)
+
+type AnthropicDriver struct {
+	httpClient *http.Client
+}
+
+var _ Driver = (*AnthropicDriver)(nil)
+
+const (
+	anthropicUsersEndpoint = "https://api.anthropic.com/v1/organizations/users"
+	// anthropicAPIVersion is the required anthropic-version header value
+	// sent on every Admin API request. Shared with the name resolver.
+	anthropicAPIVersion = "2023-06-01"
+)
+
+type anthropicUsersResponse struct {
+	Data []struct {
+		ID      string `json:"id"`
+		Email   string `json:"email"`
+		Name    string `json:"name"`
+		Role    string `json:"role"`
+		AddedAt string `json:"added_at"`
+	} `json:"data"`
+	HasMore bool   `json:"has_more"`
+	LastID  string `json:"last_id"`
+}
+
+func NewAnthropicDriver(httpClient *http.Client) *AnthropicDriver {
+	return &AnthropicDriver{
+		httpClient: httpClient,
+	}
+}
+
+func (d *AnthropicDriver) ListAccounts(ctx context.Context) ([]AccountRecord, error) {
+	var (
+		records []AccountRecord
+		afterID string
+	)
+
+	for range maxPaginationPages {
+		resp, err := d.fetchUsers(ctx, afterID)
+		if err != nil {
+			return nil, err
+		}
+
+		for _, u := range resp.Data {
+			record := AccountRecord{
+				Email:       u.Email,
+				FullName:    u.Name,
+				Role:        anthropicRole(u.Role),
+				IsAdmin:     u.Role == "admin",
+				ExternalID:  u.ID,
+				MFAStatus:   coredata.MFAStatusUnknown,
+				AuthMethod:  coredata.AccessEntryAuthMethodUnknown,
+				AccountType: coredata.AccessEntryAccountTypeUser,
+			}
+
+			// added_at is an RFC 3339 datetime string; ignore parse
+			// failures rather than dropping the record.
+			if u.AddedAt != "" {
+				if t, err := time.Parse(time.RFC3339, u.AddedAt); err == nil {
+					record.CreatedAt = &t
+				}
+			}
+
+			if record.Email != "" {
+				records = append(records, record)
+			}
+		}
+
+		if !resp.HasMore || resp.LastID == "" {
+			return records, nil
+		}
+
+		afterID = resp.LastID
+	}
+
+	return nil, fmt.Errorf("cannot list all anthropic accounts: %w", ErrPaginationLimitReached)
+}
+
+func (d *AnthropicDriver) fetchUsers(ctx context.Context, afterID string) (*anthropicUsersResponse, error) {
+	req, err := http.NewRequestWithContext(ctx, http.MethodGet, anthropicUsersEndpoint, nil)
+	if err != nil {
+		return nil, fmt.Errorf("cannot create anthropic users request: %w", err)
+	}
+
+	q := req.URL.Query()
+	q.Set("limit", "100")
+
+	if afterID != "" {
+		q.Set("after_id", afterID)
+	}
+
+	req.URL.RawQuery = q.Encode()
+
+	req.Header.Set("Accept", "application/json")
+	req.Header.Set("anthropic-version", anthropicAPIVersion)
+
+	httpResp, err := d.httpClient.Do(req)
+	if err != nil {
+		return nil, fmt.Errorf("cannot execute anthropic users request: %w", err)
+	}
+
+	defer func() {
+		_ = httpResp.Body.Close()
+	}()
+
+	if httpResp.StatusCode < 200 || httpResp.StatusCode >= 300 {
+		return nil, fmt.Errorf("cannot fetch anthropic users: unexpected status %d", httpResp.StatusCode)
+	}
+
+	var resp anthropicUsersResponse
+	if err := json.NewDecoder(httpResp.Body).Decode(&resp); err != nil {
+		return nil, fmt.Errorf("cannot decode anthropic users response: %w", err)
+	}
+
+	return &resp, nil
+}
+
+func anthropicRole(role string) string {
+	switch role {
+	case "admin":
+		return "Admin"
+	case "billing":
+		return "Billing"
+	case "developer":
+		return "Developer"
+	case "claude_code_user":
+		return "Claude Code User"
+	case "user":
+		return "User"
+	default:
+		return role
+	}
+}