diff --git a/src/RestSharp/Authenticators/OAuth/OAuth1Authenticator.cs b/src/RestSharp/Authenticators/OAuth/OAuth1Authenticator.cs
index f1a02be30..7b3384c56 100644
--- a/src/RestSharp/Authenticators/OAuth/OAuth1Authenticator.cs
+++ b/src/RestSharp/Authenticators/OAuth/OAuth1Authenticator.cs
@@ -12,15 +12,13 @@
 //   See the License for the specific language governing permissions and
 //   limitations under the License. 
 
+using JetBrains.Annotations;
+using RestSharp.Authenticators.OAuth;
+using RestSharp.Extensions;
 using System;
 using System.Collections.Generic;
 using System.Linq;
-using System.Text;
 using System.Web;
-using JetBrains.Annotations;
-using RestSharp.Authenticators.OAuth;
-using RestSharp.Authenticators.OAuth.Extensions;
-using RestSharp.Extensions;
 
 // ReSharper disable CheckNamespace
 
@@ -42,7 +40,7 @@ public class OAuth1Authenticator : IAuthenticator
 
         internal virtual string ConsumerKey { get; set; }
 
-        internal virtual string ConsumerSecret { get; set; }
+        internal virtual string? ConsumerSecret { get; set; }
 
         internal virtual string Token { get; set; }
 
@@ -84,7 +82,7 @@ public void Authenticate(IRestClient client, IRestRequest request)
 
         public static OAuth1Authenticator ForRequestToken(
             string consumerKey,
-            string consumerSecret,
+            string? consumerSecret,
             OAuthSignatureMethod signatureMethod = OAuthSignatureMethod.HmacSha1
         )
         {
@@ -101,7 +99,7 @@ public static OAuth1Authenticator ForRequestToken(
             return authenticator;
         }
 
-        public static OAuth1Authenticator ForRequestToken(string consumerKey, string consumerSecret, string callbackUrl)
+        public static OAuth1Authenticator ForRequestToken(string consumerKey, string? consumerSecret, string callbackUrl)
         {
             var authenticator = ForRequestToken(consumerKey, consumerSecret);
 
@@ -112,7 +110,7 @@ public static OAuth1Authenticator ForRequestToken(string consumerKey, string con
 
         public static OAuth1Authenticator ForAccessToken(
             string consumerKey,
-            string consumerSecret,
+            string? consumerSecret,
             string token,
             string tokenSecret,
             OAuthSignatureMethod signatureMethod = OAuthSignatureMethod.HmacSha1
@@ -131,7 +129,7 @@ public static OAuth1Authenticator ForAccessToken(
 
         public static OAuth1Authenticator ForAccessToken(
             string consumerKey,
-            string consumerSecret,
+            string? consumerSecret,
             string token,
             string tokenSecret,
             string verifier
@@ -155,7 +153,7 @@ string verifier
         /// <returns></returns>
         public static OAuth1Authenticator ForAccessTokenRefresh(
             string consumerKey,
-            string consumerSecret,
+            string? consumerSecret,
             string token,
             string tokenSecret,
             string sessionHandle
@@ -180,7 +178,7 @@ string sessionHandle
         /// <returns></returns>
         public static OAuth1Authenticator ForAccessTokenRefresh(
             string consumerKey,
-            string consumerSecret,
+            string? consumerSecret,
             string token,
             string tokenSecret,
             string verifier,
@@ -206,7 +204,7 @@ string sessionHandle
         /// <returns></returns>
         public static OAuth1Authenticator ForClientAuthentication(
             string consumerKey,
-            string consumerSecret,
+            string? consumerSecret,
             string username,
             string password,
             OAuthSignatureMethod signatureMethod = OAuthSignatureMethod.HmacSha1
@@ -234,7 +232,7 @@ public static OAuth1Authenticator ForClientAuthentication(
         /// <returns></returns>
         public static OAuth1Authenticator ForProtectedResource(
             string consumerKey,
-            string consumerSecret,
+            string? consumerSecret,
             string accessToken,
             string accessTokenSecret,
             OAuthSignatureMethod signatureMethod = OAuthSignatureMethod.HmacSha1
diff --git a/src/RestSharp/Authenticators/OAuth/OAuthTools.cs b/src/RestSharp/Authenticators/OAuth/OAuthTools.cs
index 9fa723f8b..bc9c36c9f 100644
--- a/src/RestSharp/Authenticators/OAuth/OAuthTools.cs
+++ b/src/RestSharp/Authenticators/OAuth/OAuthTools.cs
@@ -15,7 +15,6 @@
 using System;
 using System.Collections.Generic;
 using System.Linq;
-using System.Runtime.Serialization;
 using System.Security.Cryptography;
 using System.Text;
 using RestSharp.Authenticators.OAuth.Extensions;
@@ -209,7 +208,7 @@ public static string ConcatenateRequestElements(string method, string url, WebPa
         public static string GetSignature(
             OAuthSignatureMethod signatureMethod,
             string signatureBase,
-            string consumerSecret
+            string? consumerSecret
         )
             => GetSignature(signatureMethod, OAuthSignatureTreatment.Escaped, signatureBase, consumerSecret, null);
 
@@ -226,7 +225,7 @@ public static string GetSignature(
             OAuthSignatureMethod signatureMethod,
             OAuthSignatureTreatment signatureTreatment,
             string signatureBase,
-            string consumerSecret
+            string? consumerSecret
         )
             => GetSignature(signatureMethod, signatureTreatment, signatureBase, consumerSecret, null);
 
@@ -243,14 +242,15 @@ public static string GetSignature(
             OAuthSignatureMethod signatureMethod,
             OAuthSignatureTreatment signatureTreatment,
             string signatureBase,
-            string consumerSecret,
+            string? consumerSecret,
             string? tokenSecret
         )
         {
-            if (tokenSecret.IsEmpty()) tokenSecret = string.Empty;
+            if (tokenSecret.IsEmpty()) tokenSecret       = string.Empty;
+            if (consumerSecret.IsEmpty()) consumerSecret = string.Empty;
 
-            var unencodedConsumerSecret = consumerSecret;
-            consumerSecret = Uri.EscapeDataString(consumerSecret);
+            var unencodedConsumerSecret = consumerSecret!;
+            consumerSecret = Uri.EscapeDataString(consumerSecret!);
             tokenSecret    = Uri.EscapeDataString(tokenSecret!);
 
             var signature = signatureMethod switch
diff --git a/src/RestSharp/Authenticators/OAuth/OAuthWorkflow.cs b/src/RestSharp/Authenticators/OAuth/OAuthWorkflow.cs
index 236d74465..fda86f945 100644
--- a/src/RestSharp/Authenticators/OAuth/OAuthWorkflow.cs
+++ b/src/RestSharp/Authenticators/OAuth/OAuthWorkflow.cs
@@ -13,7 +13,6 @@
 //   limitations under the License.
 
 using System;
-using System.Collections.Generic;
 using System.Linq;
 using System.Web;
 using RestSharp.Authenticators.OAuth.Extensions;
@@ -31,7 +30,7 @@ sealed class OAuthWorkflow
 
         public string ConsumerKey { get; set; }
 
-        public string ConsumerSecret { get; set; }
+        public string? ConsumerSecret { get; set; }
 
         public string Token { get; set; }
 
@@ -179,14 +178,12 @@ void ValidateTokenRequestState()
         {
             Ensure.NotEmpty(RequestTokenUrl, nameof(RequestTokenUrl));
             Ensure.NotEmpty(ConsumerKey, nameof(ConsumerKey));
-            Ensure.NotEmpty(ConsumerSecret, nameof(ConsumerSecret));
         }
 
         void ValidateAccessRequestState()
         {
             Ensure.NotEmpty(AccessTokenUrl, nameof(AccessTokenUrl));
             Ensure.NotEmpty(ConsumerKey, nameof(ConsumerKey));
-            Ensure.NotEmpty(ConsumerSecret, nameof(ConsumerSecret));
             Ensure.NotEmpty(Token, nameof(Token));
         }
 
@@ -194,14 +191,12 @@ void ValidateClientAuthAccessRequestState()
         {
             Ensure.NotEmpty(AccessTokenUrl, nameof(AccessTokenUrl));
             Ensure.NotEmpty(ConsumerKey, nameof(ConsumerKey));
-            Ensure.NotEmpty(ConsumerSecret, nameof(ConsumerSecret));
             Ensure.NotEmpty(ClientUsername, nameof(ClientUsername));
         }
 
         void ValidateProtectedResourceState()
         {
             Ensure.NotEmpty(ConsumerKey, nameof(ConsumerKey));
-            Ensure.NotEmpty(ConsumerSecret, nameof(ConsumerSecret));
         }
 
         WebPairCollection GenerateAuthParameters(string timestamp, string nonce)
diff --git a/test/RestSharp.Tests/OAuth1AuthenticatorTests.cs b/test/RestSharp.Tests/OAuth1AuthenticatorTests.cs
index 9616b29b7..71af9b506 100644
--- a/test/RestSharp.Tests/OAuth1AuthenticatorTests.cs
+++ b/test/RestSharp.Tests/OAuth1AuthenticatorTests.cs
@@ -166,5 +166,36 @@ public void Authenticate_ShouldEncodeOAuthTokenParameter(OAuthType type,string v
             Assert.IsNotNull(authHeader);
             Assert.IsTrue(authHeader.Contains($"oauth_token=\"{expected}\""));
         }
+
+        /// <summary>
+        /// According the specifications of OAuth 1.0a, the customer secret is not required.
+        /// For more information, check the section 4 on https://oauth.net/core/1.0a/.
+        /// </summary>
+        [Test]
+        [TestCase(OAuthType.AccessToken)]
+        [TestCase(OAuthType.ProtectedResource)]
+        [TestCase(OAuthType.AccessToken)]
+        [TestCase(OAuthType.ProtectedResource)]
+        public void Authenticate_ShouldAllowEmptyConsumerSecret_OnHttpAuthorizationHeaderHandling(OAuthType type)
+        { 
+            // Arrange
+            const string url = "https://no-query.string";
+
+            var client  = new RestClient(url);
+            var request = new RestRequest();
+            _authenticator.Type           = type;
+            _authenticator.ConsumerSecret = null;
+            
+            // Act
+            _authenticator.Authenticate(client, request);
+
+            // Assert
+            var authParameter = request.Parameters.Single(x => x.Name == "Authorization");
+            var value = (string)authParameter.Value;
+            
+            Assert.IsNotEmpty(value);
+            Assert.IsTrue(value!.Contains("OAuth"));
+            Assert.IsTrue(value.Contains("oauth_signature=\"" + OAuthTools.UrlEncodeStrict("&")));
+        }
     }
 }