diff --git a/pkg/artifacts/artifacts_v4.go b/pkg/artifacts/artifacts_v4.go
index 9cbe0b3c863..ea8075a0917 100644
--- a/pkg/artifacts/artifacts_v4.go
+++ b/pkg/artifacts/artifacts_v4.go
@@ -210,16 +210,28 @@ func (r artifactV4Routes) buildSignature(endp, expires, artifactName string, tas
 func (r artifactV4Routes) buildArtifactURL(endp, artifactName string, taskID int64) string {
 	expires := time.Now().Add(60 * time.Minute).Format("2006-01-02 15:04:05.999999999 -0700 MST")
 	uploadURL := "http://" + strings.TrimSuffix(r.AppURL, "/") + strings.TrimSuffix(r.prefix, "/") +
-		"/" + endp + "?sig=" + base64.URLEncoding.EncodeToString(r.buildSignature(endp, expires, artifactName, taskID)) + "&expires=" + url.QueryEscape(expires) + "&artifactName=" + url.QueryEscape(artifactName) + "&taskID=" + fmt.Sprint(taskID)
+		"/" + endp + "?sig=" + base64.RawURLEncoding.EncodeToString(r.buildSignature(endp, expires, artifactName, taskID)) + "&expires=" + url.QueryEscape(expires) + "&artifactName=" + url.QueryEscape(artifactName) + "&taskID=" + fmt.Sprint(taskID)
 	return uploadURL
 }
 
+func decodeBase64URLSignature(sig string) ([]byte, error) {
+	if decoded, err := base64.RawURLEncoding.DecodeString(sig); err == nil {
+		return decoded, nil
+	}
+	return base64.URLEncoding.DecodeString(sig)
+}
+
 func (r artifactV4Routes) verifySignature(ctx *ArtifactContext, endp string) (int64, string, bool) {
 	rawTaskID := ctx.Req.URL.Query().Get("taskID")
 	sig := ctx.Req.URL.Query().Get("sig")
 	expires := ctx.Req.URL.Query().Get("expires")
 	artifactName := ctx.Req.URL.Query().Get("artifactName")
-	dsig, _ := base64.URLEncoding.DecodeString(sig)
+	dsig, err := decodeBase64URLSignature(sig)
+	if err != nil {
+		log.Error("Error unauthorized")
+		ctx.Error(http.StatusUnauthorized, "Error unauthorized")
+		return -1, "", false
+	}
 	taskID, _ := strconv.ParseInt(rawTaskID, 10, 64)
 
 	expecedsig := r.buildSignature(endp, expires, artifactName, taskID)
diff --git a/pkg/artifacts/server_test.go b/pkg/artifacts/server_test.go
index 0591fbb9987..943da53c879 100644
--- a/pkg/artifacts/server_test.go
+++ b/pkg/artifacts/server_test.go
@@ -6,6 +6,7 @@ import (
 	"fmt"
 	"net/http"
 	"net/http/httptest"
+	"net/url"
 	"os"
 	"path"
 	"path/filepath"
@@ -393,3 +394,44 @@ func TestArtifactUploadBlobUnsafePath(t *testing.T) {
 	assert.Equal("success", response.Message)
 	assert.Equal("content", string(memfs["artifact/server/path/1/some/file"].Data))
 }
+
+func TestArtifactV4BuildArtifactURLUsesRawBase64Signature(t *testing.T) {
+	assert := assert.New(t)
+
+	route := artifactV4Routes{
+		prefix: ArtifactV4RouteBase,
+		AppURL: "localhost",
+	}
+
+	uploadURL, err := url.Parse(route.buildArtifactURL("UploadArtifact", "test-artifact", 1))
+	assert.NoError(err)
+	assert.NotContains(uploadURL.Query().Get("sig"), "=")
+}
+
+func TestArtifactV4UploadAcceptsUnpaddedBase64Signature(t *testing.T) {
+	assert := assert.New(t)
+
+	var memfs = fstest.MapFS(map[string]*fstest.MapFile{})
+	route := artifactV4Routes{
+		fs:      writeMapFS{memfs},
+		rfs:     memfs,
+		baseDir: "artifact/server/path",
+		prefix:  ArtifactV4RouteBase,
+		AppURL:  "localhost",
+	}
+
+	uploadURL, err := url.Parse(route.buildArtifactURL("UploadArtifact", "test-artifact", 1))
+	assert.NoError(err)
+	query := uploadURL.Query()
+	query.Set("sig", strings.TrimRight(query.Get("sig"), "="))
+	query.Set("comp", "block")
+	uploadURL.RawQuery = query.Encode()
+
+	req, _ := http.NewRequest("PUT", uploadURL.String(), strings.NewReader("content"))
+	rr := httptest.NewRecorder()
+
+	route.uploadArtifact(&ArtifactContext{Req: req, Resp: rr})
+
+	assert.Equal(http.StatusCreated, rr.Code)
+	assert.Equal("content", string(memfs["artifact/server/path/1/test-artifact/test-artifact.zip"].Data))
+}