~fix tenant regex validation

+add method to set defaultrequestheader
+add testcases

Author: smolny-marko

src/Serilog.Sinks.Grafana.Loki/HttpClients/BaseLokiHttpClient.cs

@@ -33,7 +33,7 @@ public abstract class BaseLokiHttpClient : ILokiHttpClient
     /// <summary>
     /// Regex for Tenant ID validation.
     /// </summary>
-    private static readonly Regex TenantIdValueRegex = new Regex(@"^[a-zA-Z0-9]*$");
+    private static readonly Regex TenantIdValueRegex = new Regex(@"^(?!.*\.\.)(?!\.$)[a-zA-Z0-9!._*'()\-\u005F]*$");
 
     /// <summary>
     /// Initializes a new instance of the <see cref="BaseLokiHttpClient"/> class.
@@ -91,6 +91,28 @@ public virtual void SetTenant(string? tenant)
         headers.Add(TenantHeader, tenant);
     }
 
+    /// <summary>
+    /// Sets default headers for the HTTP client.
+    /// Existing headers with the same key will not be overwritten.
+    /// </summary>
+    /// <param name="defaultHeaders">A dictionary of headers to set as default.</param>
+    public virtual void SetDefaultHeaders(IDictionary<string, string> defaultHeaders)
+    {
+        if (defaultHeaders == null)
+        {
+            throw new ArgumentNullException(nameof(defaultHeaders), "Default headers cannot be null.");
+        }
+
+        foreach (var header in defaultHeaders)
+        {
+            // Check if the header already exists before adding
+            if (!HttpClient.DefaultRequestHeaders.Contains(header.Key))
+            {
+                HttpClient.DefaultRequestHeaders.Add(header.Key, header.Value);
+            }
+        }
+    }
+
     /// <inheritdoc/>
     public virtual void Dispose() => HttpClient.Dispose();
 

test/Serilog.Sinks.Grafana.Loki.Tests/HttpClientsTests/BaseLokiHttpClientTests.cs

@@ -51,13 +51,35 @@ public void AuthorizationHeaderShouldNotBeSetWithoutCredentials()
     [Fact]
     public void TenantHeaderShouldBeCorrect()
     {
-        var tenantId = "lokitenant";
-        using var client = new TestLokiHttpClient();
-
-        client.SetTenant(tenantId);
-
-        var tenantHeaders = client.Client.DefaultRequestHeaders.GetValues("X-Scope-OrgID").ToList();
-        tenantHeaders.ShouldBeEquivalentTo(new List<string> {"lokitenant"});
+        // List of test cases with tenant IDs and their expected validity
+        var validTenantIds = new List<(string TenantId, bool IsValid)>
+    {
+        ("tenant123", true), // Only alphanumeric characters
+        ("tenant-123", true), // Valid special characters
+        ("tenant..123", false), // Double period ".." is not allowed
+        (".", false), // Single period is not allowed
+        ("tenant!_*.123'()", true), // All allowed special characters
+        ("tenant-123...", false), // Multiple periods at the end are not allowed
+        ("tenant123456...test", false), // Ends with a period "."
+        ("tenant1234567890!@", false), // "@" is not allowed
+    };
+
+        foreach (var (tenantId, isValid) in validTenantIds)
+        {
+            using var client = new TestLokiHttpClient();
+
+            if (isValid)
+            {
+                client.SetTenant(tenantId);
+
+                var tenantHeaders = client.Client.DefaultRequestHeaders.GetValues("X-Scope-OrgID").ToList();
+                tenantHeaders.ShouldBeEquivalentTo(new List<string> { tenantId });
+            }
+            else
+            {
+                Should.Throw<ArgumentException>(() => client.SetTenant(tenantId));
+            }
+        }
     }
 
     [Fact]
@@ -78,4 +100,24 @@ public void TenantHeaderShouldThrowAnExceptionOnTenantIdAgainstRule()
 
         Should.Throw<ArgumentException>(() => client.SetTenant(tenantId));
     }
+
+    [Fact]
+    public void SetDefaultHeadersShouldSetHeaderCorrectly()
+    {
+        // Arrange
+        using var httpClient = new HttpClient();
+        var client = new TestLokiHttpClient(httpClient);
+
+        var headersToSet = new Dictionary<string, string>
+        {
+            { "Custom-Header", "HeaderValue" }
+        };
+
+        // Act
+        client.SetDefaultHeaders(headersToSet);
+
+        // Assert
+        httpClient.DefaultRequestHeaders.Contains("Custom-Header").ShouldBeTrue();
+        httpClient.DefaultRequestHeaders.GetValues("Custom-Header").ShouldBe(new[] { "HeaderValue" });
+    }
 }