diff --git a/browser/src/control/Control.ESignature.ts b/browser/src/control/Control.ESignature.ts
index 7545675f521f..e94f0f6a12a3 100644
--- a/browser/src/control/Control.ESignature.ts
+++ b/browser/src/control/Control.ESignature.ts
@@ -23,6 +23,11 @@ namespace cool {
 		doc_id: string;
 	}
 
+	export interface SignedResponse {
+		type: string;
+		error: string;
+	}
+
 	/**
 	 * Provides electronic signing with document hashes for PDF files.
 	 */
@@ -33,14 +38,23 @@ namespace cool {
 		// <https://docs.eideasy.com/guide/api-credentials.html>
 		secret: string;
 		clientId: string;
+		// This is the specific provider used by eIDEasy, e.g. 'smart-id-signature'
+		method: string;
 
 		// Timestamp of the hash extraction
 		signatureTime: number;
 
-		constructor(url: string, secret: string, clientId: string) {
+		// Identifier of the document on the eIDEasy side
+		docId: string;
+
+		// The popup window we opened.
+		popup: Window;
+
+		constructor(url: string, secret: string, clientId: string, method: string) {
 			this.url = url;
 			this.secret = secret;
 			this.clientId = clientId;
+			this.method = method;
 
 			app.map.on('commandvalues', this.onCommandValues.bind(this));
 		}
@@ -119,11 +133,38 @@ namespace cool {
 
 		// Handles the 'send hash' response JSON
 		handleSendHashJson(response: HashSendResponse): void {
-			const docId = response.doc_id;
+			this.docId = response.doc_id;
+
+			let url = this.url + '/single-method-signature';
+			url += '?client_id=' + this.clientId;
+			url += '&doc_id=' + this.docId;
+			url += '&method=' + this.method;
+
+			let features = 'popup';
+			features += ', left=' + window.screen.width / 4;
+			features += ', top=' + window.screen.height / 4;
+			features += ', width=' + window.screen.width / 2;
+			features += ', height=' + window.screen.height / 2;
+
+			// Step 3: sign the hash.
+			this.popup = window.open(url, '_blank', features);
+		}
+
+		// Handles the 'sign hash' response
+		handleSigned(response: SignedResponse): void {
+			if (response.type != 'SUCCESS') {
+				app.console.log('failed to sign: ' + response.error);
+				return;
+			}
+
+			try {
+				this.popup.close();
+			} catch (error) {
+				app.console.log('failed to close the signing popup: ' + error.message);
+			}
+
 			console.log(
-				'TODO(vmiklos) ESignature::handleSendHashJson: docId is "' +
-					docId +
-					'"',
+				'TODO(vmiklos) ESignature::handleSigned: fetch the signature',
 			);
 		}
 	}
@@ -135,6 +176,7 @@ L.control.eSignature = function (
 	url: string,
 	secret: string,
 	clientId: string,
+	method: string,
 ) {
-	return new L.Control.ESignature(url, secret, clientId);
+	return new L.Control.ESignature(url, secret, clientId, method);
 };
diff --git a/browser/src/control/Control.UIManager.js b/browser/src/control/Control.UIManager.js
index 614788b6c70e..c2f25f2144b1 100644
--- a/browser/src/control/Control.UIManager.js
+++ b/browser/src/control/Control.UIManager.js
@@ -1077,8 +1077,9 @@ L.Control.UIManager = L.Control.extend({
 			const baseUrl = userPrivateInfo.ESignatureBaseUrl;
 			const secret = userPrivateInfo.ESignatureSecret;
 			const clientId = userPrivateInfo.ESignatureClientId;
+			const method = userPrivateInfo.ESignatureMethod;
 			if (baseUrl !== undefined && !this.map.eSignature) {
-				this.map.eSignature = L.control.eSignature(baseUrl, secret, clientId);
+				this.map.eSignature = L.control.eSignature(baseUrl, secret, clientId, method);
 			}
 		}
 	},
diff --git a/browser/src/map/handler/Map.WOPI.js b/browser/src/map/handler/Map.WOPI.js
index b83c959f504f..67e53ce436a4 100644
--- a/browser/src/map/handler/Map.WOPI.js
+++ b/browser/src/map/handler/Map.WOPI.js
@@ -263,6 +263,12 @@ L.Map.WOPI = L.Handler.extend({
 			return true;
 		}
 
+		const eSignature = this._map.eSignature;
+		if (eSignature && eSignature.url === e.origin) {
+			// The sender is our esign popup: accept it.
+			return true;
+		}
+
 		return false;
 	},
 
@@ -277,6 +283,9 @@ L.Map.WOPI = L.Handler.extend({
 		if (('data' in e) && Object.hasOwnProperty.call(e.data, 'MessageId')) {
 			// when e.data already contains the right props, but isn't JSON (a blob is passed for ex)
 			msg = e.data;
+		} else if (typeof e.data === 'object') {
+			// E.g. the esign popup sends us an object, no need to JSON-parse it.
+			msg = e.data;
 		} else {
 			try {
 				msg = JSON.parse(e.data);
@@ -684,6 +693,13 @@ L.Map.WOPI = L.Handler.extend({
 			var list = msg.Values.list;
 			this._map.mention.openMentionPopup(list);
 		}
+		else if (msg.sender === 'EIDEASY_SINGLE_METHOD_SIGNATURE') {
+			// This is produced by the esign popup.
+			const eSignature = this._map.eSignature;
+			if (eSignature) {
+				eSignature.handleSigned(msg);
+			}
+		}
 	},
 
 	_postMessage: function(e) {