Sending Messages to Teams Channels via Bot Without adding into Team in Microsoft Teams

Question

Is it possible to send messages to specific channels in Microsoft Teams from a bot without adding the bot to each team?

The use case involves allowing users to select channels they are part of, and then, upon clicking send, the bot would deliver an adaptive card to all selected channels.

I attempted to obtain the bot's access token and used the Graph API to send messages to the channel, but encountered an "Unauthorized" error with the message: "Message POST is allowed in application-only context only for import purposes." The documentation suggests that for sending messages to a channel in a team, the bot must be added to that team, which is inconvenient for this scenario.

Is there a way to send messages to a channel without having to add the bot to each team?

Answer 1

If you have necessary permission for application, I think it is possible to send message to teams channel via on behalf of application via Graph API. Here is steps: Obtain token via client_credentials:

import requests
# Azure AD credentials
tenant_id = "your-tenant-id"
client_id = "your-client-id"
client_secret = "your-client-secret"
# Token endpoint
url = f"https://login.microsoftonline.com/{tenant_id}/oauth2/v2.0/token"
# Request body
data = {
    "grant_type": "client_credentials",
    "client_id": client_id,
    "client_secret": client_secret,
    "scope": "https://graph.microsoft.com/.default"
}
response = requests.post(url, data=data)
access_token = response.json().get("access_token")

Send message to channel:

# Teams API endpoint
team_id = "your-team-id"
channel_id = "your-channel-id"
url = f"https://graph.microsoft.com/v1.0/teams/{team_id}/channels/{channel_id}/messages"
# Message content
headers = {
    "Authorization": f"Bearer {access_token}",
    "Content-Type": "application/json"
}
payload = {
    "body": {
        "content": "Hello, this is a message sent by an application!"
    }
}
response = requests.post(url, json=payload, headers=headers)
if response.status_code == 201:
    print("Message sent successfully!")
else:
    print("Error:", response.json())