The goal is still to create a process which get a random cat picture and post it on a yammer group daily. Last week I tried with the Yammer connector available in MS flow but it does not support posting image as I explain in https://djynet.net/?p=945 . This time I decided to go one level deeper and us the Yammer REST API which support it. 

Yammer REST API 

We want to use the /messages POST REST call describe in the official REST API doc here: https://developer.yammer.com/docs/messages-json-post which mention the support of attachments “Yammer provides two methods to associate attachments with a message. Both make use of multi-part HTTP upload (see RFC1867)”. 

To be able to post we need to Authentify our self with the yammer Oauth2 flow describe here: https://developer.yammer.com/docs/oauth-2. I don t want to detail it too much since it’s pretty standard but basically our server offers and /login route which redirect to yammer.com.  

 app.get('/login', (req, res) => {
    var aLoginUri = "https://www.yammer.com/oauth2/authorize?client_id=CN737QnN3TCu2ooY7U2rbA&response_type=code&redirect_uri=https://djynet.xyz/callback";
    console.log('Sent login URI response');

Then yammer.com call redirect back the user to our server on /callback route with a user token we can use from our server when querying the yammer.com API to post messages. 

 // OAuth2 endpoint (callback)
app.get('/callback', (req, res) => {
    console.log('Received Oauth login callback with code ' + req.url);

    //Calling Oauth to authenticate the APP
    var aUriAuthent = "https://www.yammer.com/oauth2/access_token?client_id=CN737QnN3TCu2ooY7U2rbA&client_secret=" + aClientSecret + "&code=" + req.query.code + "&grant_type=authorization_code";
        .then((res) => {
            //console.log("Dumping response for debuging: " +res)
            //console.log("Dumping data from response for Debug: ", res.data)
            aAUthTest2 = res.data;
        .catch((error) => {

Getting random cat picture 

Of course there is an API for that 😉 https://thecatapi.com/ The API is free but you need to register to get a API KEY that you specify in your header when calling with ‘x-api-key’. The endpoint we need is https://api.thecatapi.com/v1/images/search that we call without any parameters and will give us a random cat url.  

 async function getCatUrl() {
    console.log('Entering getCatUrl');
    var aCatUrl = "https://upload.wikimedia.org/wikipedia/commons/4/4d/Cat_November_2010-1a.jpg";
    const aTemp = await axios.get("https://api.thecatapi.com/v1/images/search", { params: {}, headers: { 'x-api-key': aCatApiKey } });
    aCatUrl = aTemp.data[0].url
    console.log('Existing getCatUrl with: ', aCatUrl);
    return aCatUrl;

One note here is the use of async/await for us to “wait” the response of catApi before we can proceed and post our picture in the yammer room. I will not detail await/asynch….so many good doc already (google it) 

Posting the image 

We now have a token and a cat picture URL that we can use to post our message. This is the only complicated part of this whole project due to “Both make use of multi-part HTTP upload (see RFC1867)”. I find this NPM module which should make this process easier: https://www.npmjs.com/package/form-data that we can use to create the “multipart/form-data” and then give to another module to send it to Yammer API. Here is the form part 

var formData = new FormData(); 
formData.append('attachment1', Request(aCatUrl));  

Which is quite straightforward as explain in their readme. Then we pass the form to another node module to send 


The first module I tried to use to post the REST call is AXIOS: https://www.npmjs.com/package/axios which we use to get the random cat picture. Nevertheless, the documentation of form-data to use AXIOS has a bug which I was unable to understand so I open a bug report and switch to another library than Axios. The bug has now been fixed by a documentation change: https://github.com/form-data/form-data/issues/439 


Instead of axios we can use the native HTTPS nodejs module describe here: https://nodejs.org/api/https.html and pass him our form:  

// Patch header to add the key
var aHeader = formData.getHeaders();
aHeader['Authorization'] = "Bearer " + aAUthTest2.access_token.token;

var request = https.request({
    method: 'post',
    host: 'www.yammer.com',
    //very dirty.... did not find a way to pass param otherwise :(
    path: '/api/v1/messages.json?body=Cat%20of%20the%20day%20&group_id=7799980032',
    headers: aHeader

//send it

Final touch 

I added a secret key in the postcat route to ensure nobody else will use it to spam the room with cat 

 if (req.query.key !== aPostCatSecretKey) {
        console.log("Invalid key: ",req.query.key," - send back 401")

And then I added a crontab to call our API everyday 

0 1 * * * curl https://djynet.xyz/postcat?key=mysecretkey 

All code is here: https://bitbucket.org/charly37/catyammer/src/master/ 

And the result:  

Yammer connector

The goal is to create a MS office 365 Flow which will call a homemade connector to get a random cat picture and post it on a yammer group. 

Yammer connector 

The first thing to do is check if there is a MS Office365 connector that can get use a random cat picture (who know…. Maybe someone already done one). After checking https://flow.microsoft.com/en-us/connectors/ it seems it s not the case. So we have to create one.  

I will not go too much in the details since the MS doc is quite good https://docs.microsoft.com/en-us/connectors/custom-connectors/define-openapi-definition. One interesting point was the fact it needs to be HTTPS so I played with Let’s encrypt and their docker version of certbot…. Nothing fancy apart that…. classical NodeJS server with only one endpoint with an hardcode to start with 

app.get(‘/v2/cat’, (req,res) => { 

var aCatUrl = “https://i.imgur.com/x7X0Fxf.jpg“; 


console.log(‘Sent response’); 


The full code is here https://bitbucket.org/charly37/catpy/src/master/ 

Once the connector is ready to be used you can validate it with a quick postman call like: 

Then you can add it on your MS 365 personal connector as explain in the MS doc. I used the “from OpenApi file” method with the following file https://bitbucket.org/charly37/catpy/src/master/myapp/swagger.json 

Flow creation 

Now that the connector is publish on your Office365 space you can create a flow using it. I copy past and existing template “Post an update to my company’s Yammer page” that I customize with an extra step to call my connector and post the response of the connector into the yammer room 

Then you can test it and see that the result is not exactly what we excepted…. 

I was hoping to have the picture posted on yammer like it is the case when I post the URL myself on the UI like  

The reason why it did not work is that the YAMMER connector do not allow to post picture. There is already an open request on MS side so that it is supported in the future (feel free to vote for it) here: https://powerusers.microsoft.com/t5/Flow-Ideas/Post-on-Yammer-with-image-attachments/idi-p/14300


I will wait until MS implement that like I done for the JS function in Excel online 😉 and in the meantime I will try to do a REST call directly to Yammer API to see if I can post an image directly (without going throw flow). 

Let’s encrypt TLS setup for nodejs

Following my first test to setup a HTTPS server to dialogue with facebook API describe in my previous article here I had error when trying to register the facebook webhook:


I dig deeper and also verified the domain certificate with https://www.ssllabs.com/ssltest :


It seems good but there is a warning about the certificate chain… I done some quick research and it seem to be the root cause. After some investigation (and mainly thanks to this post) it seems the error comes from my nodejs server setup and more particularly the missing certificate authority certificate info. I miss it since it is not used in the official documentation. It is indeed an optional parameter

If this is omitted several well-known “root” CAs will be used, like VeriSign

Let’s add it in the options:

var options = {
    key: fs.readFileSync('/etc/letsencrypt/live/djynet.xyz/privkey.pem'),
    cert: fs.readFileSync('/etc/letsencrypt/live/djynet.xyz/cert.pem'),
    ca: fs.readFileSync('/etc/letsencrypt/live/djynet.xyz/chain.pem')

I done the ssl check another time and the error is now gone…. And the facebook webhook work fine too: