diff --git a/src/ZB.MOM.WW.ScadaBridge.Security/ScadaBridgeGroupRoleMapper.cs b/src/ZB.MOM.WW.ScadaBridge.Security/ScadaBridgeGroupRoleMapper.cs
new file mode 100644
index 00000000..02a23ee0
--- /dev/null
+++ b/src/ZB.MOM.WW.ScadaBridge.Security/ScadaBridgeGroupRoleMapper.cs
@@ -0,0 +1,40 @@
+using ZB.MOM.WW.Auth.Abstractions.Roles;
+
+namespace ZB.MOM.WW.ScadaBridge.Security;
+
+/// <summary>
+/// Adapts ScadaBridge's DB-backed <see cref="RoleMapper"/> to the shared
+/// <see cref="IGroupRoleMapper{TRole}"/> seam from <c>ZB.MOM.WW.Auth.Abstractions</c>.
+/// </summary>
+/// <remarks>
+/// Task 1.1 of the Auth-library adoption: this is an <b>additive</b> wrapper. It does not
+/// re-implement the LDAP-group → role resolution or the site-scope union semantics — it
+/// delegates wholesale to <see cref="RoleMapper.MapGroupsToRolesAsync"/> and re-shapes the
+/// result onto the shared contract. <typeparamref name="TRole"/> is <see cref="string"/>
+/// because ScadaBridge roles travel as plain strings in claims. The full
+/// <see cref="RoleMappingResult"/> — including <see cref="RoleMappingResult.PermittedSiteIds"/>
+/// and <see cref="RoleMappingResult.IsSystemWideDeployment"/> — is carried verbatim in the
+/// mapping's opaque <see cref="GroupRoleMapping{TRole}.Scope"/> so no site-scope information
+/// is lost across the seam. The existing login flow is rewired to consume this in a later task.
+/// </remarks>
+public sealed class ScadaBridgeGroupRoleMapper : IGroupRoleMapper<string>
+{
+    private readonly RoleMapper _roleMapper;
+
+    /// <summary>Initializes the mapper with the wrapped <see cref="RoleMapper"/>.</summary>
+    /// <param name="roleMapper">The DB-backed role mapper whose union semantics are reused.</param>
+    public ScadaBridgeGroupRoleMapper(RoleMapper roleMapper)
+    {
+        _roleMapper = roleMapper ?? throw new ArgumentNullException(nameof(roleMapper));
+    }
+
+    /// <inheritdoc />
+    public async Task<GroupRoleMapping<string>> MapAsync(IReadOnlyList<string> groups, CancellationToken ct)
+    {
+        var result = await _roleMapper.MapGroupsToRolesAsync(groups, ct);
+
+        // Carry the full RoleMappingResult as the opaque Scope so the site-scope
+        // payload (PermittedSiteIds + IsSystemWideDeployment) survives the seam.
+        return new GroupRoleMapping<string>(result.Roles, Scope: result);
+    }
+}
diff --git a/src/ZB.MOM.WW.ScadaBridge.Security/ServiceCollectionExtensions.cs b/src/ZB.MOM.WW.ScadaBridge.Security/ServiceCollectionExtensions.cs
index 33074a80..97c6f785 100644
--- a/src/ZB.MOM.WW.ScadaBridge.Security/ServiceCollectionExtensions.cs
+++ b/src/ZB.MOM.WW.ScadaBridge.Security/ServiceCollectionExtensions.cs
@@ -3,6 +3,7 @@ using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Extensions.DependencyInjection.Extensions;
 using Microsoft.Extensions.Logging;
 using Microsoft.Extensions.Options;
+using ZB.MOM.WW.Auth.Abstractions.Roles;
 
 namespace ZB.MOM.WW.ScadaBridge.Security;
 
@@ -18,6 +19,14 @@ public static class ServiceCollectionExtensions
         services.AddScoped<JwtTokenService>();
         services.AddScoped<RoleMapper>();
 
+        // Auth-adoption Task 1.1: register the shared IGroupRoleMapper<string>
+        // seam additively, wrapping RoleMapper to reuse its DB-backed mapping +
+        // site-scope union semantics. Scoped to match RoleMapper's lifetime (it
+        // depends on the Scoped ISecurityRepository). The existing RoleMapper
+        // registration and its call sites are left untouched — login is rewired
+        // to consume this seam in a later task.
+        services.AddScoped<IGroupRoleMapper<string>, ScadaBridgeGroupRoleMapper>();
+
         // Security-020: register the IValidateOptions<SecurityOptions> so a
         // missing/empty LdapServer or LdapSearchBase fails fast at startup
         // with a clear, key-naming message rather than a generic LDAP error
diff --git a/src/ZB.MOM.WW.ScadaBridge.Security/ZB.MOM.WW.ScadaBridge.Security.csproj b/src/ZB.MOM.WW.ScadaBridge.Security/ZB.MOM.WW.ScadaBridge.Security.csproj
index dabf2f2c..faa7131e 100644
--- a/src/ZB.MOM.WW.ScadaBridge.Security/ZB.MOM.WW.ScadaBridge.Security.csproj
+++ b/src/ZB.MOM.WW.ScadaBridge.Security/ZB.MOM.WW.ScadaBridge.Security.csproj
@@ -14,6 +14,7 @@
     <PackageReference Include="Microsoft.AspNetCore.Authorization" />
     <PackageReference Include="System.IdentityModel.Tokens.Jwt" />
     <PackageReference Include="Novell.Directory.Ldap.NETStandard" />
+    <PackageReference Include="ZB.MOM.WW.Auth.Abstractions" />
     <PackageReference Include="ZB.MOM.WW.Configuration" />
   </ItemGroup>
 
diff --git a/tests/ZB.MOM.WW.ScadaBridge.Security.Tests/ScadaBridgeGroupRoleMapperTests.cs b/tests/ZB.MOM.WW.ScadaBridge.Security.Tests/ScadaBridgeGroupRoleMapperTests.cs
new file mode 100644
index 00000000..8ae32059
--- /dev/null
+++ b/tests/ZB.MOM.WW.ScadaBridge.Security.Tests/ScadaBridgeGroupRoleMapperTests.cs
@@ -0,0 +1,127 @@
+using ZB.MOM.WW.Auth.Abstractions.Roles;
+using ZB.MOM.WW.ScadaBridge.Commons.Entities.Security;
+using ZB.MOM.WW.ScadaBridge.Commons.Interfaces.Repositories;
+using ZB.MOM.WW.ScadaBridge.Security;
+
+namespace ZB.MOM.WW.ScadaBridge.Security.Tests;
+
+#region Task 1.1: ScadaBridgeGroupRoleMapper (IGroupRoleMapper<string> seam)
+
+public class ScadaBridgeGroupRoleMapperTests
+{
+    // A minimal in-memory ISecurityRepository so the seam test needs no database.
+    // Only the two reads RoleMapper.MapGroupsToRolesAsync uses are implemented;
+    // the rest throw to make any accidental dependency on them obvious.
+    private sealed class FakeSecurityRepository : ISecurityRepository
+    {
+        private readonly IReadOnlyList<LdapGroupMapping> _mappings;
+        private readonly IReadOnlyDictionary<int, IReadOnlyList<SiteScopeRule>> _scopeRules;
+
+        public FakeSecurityRepository(
+            IReadOnlyList<LdapGroupMapping> mappings,
+            IReadOnlyDictionary<int, IReadOnlyList<SiteScopeRule>> scopeRules)
+        {
+            _mappings = mappings;
+            _scopeRules = scopeRules;
+        }
+
+        public Task<IReadOnlyList<LdapGroupMapping>> GetAllMappingsAsync(CancellationToken cancellationToken = default)
+            => Task.FromResult(_mappings);
+
+        public Task<IReadOnlyList<SiteScopeRule>> GetScopeRulesForMappingAsync(int ldapGroupMappingId, CancellationToken cancellationToken = default)
+            => Task.FromResult(_scopeRules.TryGetValue(ldapGroupMappingId, out var rules)
+                ? rules
+                : (IReadOnlyList<SiteScopeRule>)Array.Empty<SiteScopeRule>());
+
+        public Task<LdapGroupMapping?> GetMappingByIdAsync(int id, CancellationToken cancellationToken = default)
+            => throw new NotSupportedException();
+        public Task<IReadOnlyList<LdapGroupMapping>> GetMappingsByRoleAsync(string role, CancellationToken cancellationToken = default)
+            => throw new NotSupportedException();
+        public Task AddMappingAsync(LdapGroupMapping mapping, CancellationToken cancellationToken = default)
+            => throw new NotSupportedException();
+        public Task UpdateMappingAsync(LdapGroupMapping mapping, CancellationToken cancellationToken = default)
+            => throw new NotSupportedException();
+        public Task DeleteMappingAsync(int id, CancellationToken cancellationToken = default)
+            => throw new NotSupportedException();
+        public Task<SiteScopeRule?> GetScopeRuleByIdAsync(int id, CancellationToken cancellationToken = default)
+            => throw new NotSupportedException();
+        public Task AddScopeRuleAsync(SiteScopeRule rule, CancellationToken cancellationToken = default)
+            => throw new NotSupportedException();
+        public Task UpdateScopeRuleAsync(SiteScopeRule rule, CancellationToken cancellationToken = default)
+            => throw new NotSupportedException();
+        public Task DeleteScopeRuleAsync(int id, CancellationToken cancellationToken = default)
+            => throw new NotSupportedException();
+        public Task<int> SaveChangesAsync(CancellationToken cancellationToken = default)
+            => throw new NotSupportedException();
+    }
+
+    private static LdapGroupMapping Mapping(int id, string group, string role)
+    {
+        var m = new LdapGroupMapping(group, role);
+        m.Id = id;
+        return m;
+    }
+
+    [Fact]
+    public async Task MapAsync_ReturnsSameRolesAsRoleMapper_AndCarriesResultInScope_SiteScoped()
+    {
+        // Two matched mappings: an Admin group and a site-scoped Deployment group.
+        var mappings = new List<LdapGroupMapping>
+        {
+            Mapping(1, "SCADA-Admins", Roles.Admin),
+            Mapping(2, "SiteDeployers", Roles.Deployment),
+        };
+        var scopeRules = new Dictionary<int, IReadOnlyList<SiteScopeRule>>
+        {
+            [2] = new[]
+            {
+                new SiteScopeRule { LdapGroupMappingId = 2, SiteId = 11 },
+                new SiteScopeRule { LdapGroupMappingId = 2, SiteId = 22 },
+            },
+        };
+        var repo = new FakeSecurityRepository(mappings, scopeRules);
+        var roleMapper = new RoleMapper(repo);
+        var sut = new ScadaBridgeGroupRoleMapper(roleMapper);
+
+        var groups = new[] { "SCADA-Admins", "SiteDeployers" };
+
+        // The wrapped RoleMapper result is the oracle the seam must preserve.
+        var expected = await roleMapper.MapGroupsToRolesAsync(groups, CancellationToken.None);
+        var mapping = await sut.MapAsync(groups, CancellationToken.None);
+
+        // Roles: same set as RoleMapper.
+        Assert.Equal(expected.Roles.OrderBy(r => r), mapping.Roles.OrderBy(r => r));
+        Assert.Contains(Roles.Admin, mapping.Roles);
+        Assert.Contains(Roles.Deployment, mapping.Roles);
+
+        // Scope: carries the full RoleMappingResult (no site-scope info lost).
+        var scope = Assert.IsType<RoleMappingResult>(mapping.Scope);
+        Assert.False(scope.IsSystemWideDeployment);
+        Assert.Contains("11", scope.PermittedSiteIds);
+        Assert.Contains("22", scope.PermittedSiteIds);
+        Assert.Equal(expected.PermittedSiteIds.OrderBy(s => s), scope.PermittedSiteIds.OrderBy(s => s));
+        Assert.Equal(expected.IsSystemWideDeployment, scope.IsSystemWideDeployment);
+    }
+
+    [Fact]
+    public async Task MapAsync_PreservesSystemWideDeploymentFlagInScope()
+    {
+        // Unscoped Deployment mapping -> system-wide, empty PermittedSiteIds.
+        var mappings = new List<LdapGroupMapping>
+        {
+            Mapping(1, "GlobalDeployers", Roles.Deployment),
+        };
+        var repo = new FakeSecurityRepository(mappings, new Dictionary<int, IReadOnlyList<SiteScopeRule>>());
+        var roleMapper = new RoleMapper(repo);
+        var sut = new ScadaBridgeGroupRoleMapper(roleMapper);
+
+        var mapping = await sut.MapAsync(new[] { "GlobalDeployers" }, CancellationToken.None);
+
+        Assert.Contains(Roles.Deployment, mapping.Roles);
+        var scope = Assert.IsType<RoleMappingResult>(mapping.Scope);
+        Assert.True(scope.IsSystemWideDeployment);
+        Assert.Empty(scope.PermittedSiteIds);
+    }
+}
+
+#endregion