官方链接：

The Jira Cloud platform REST API

POST

Add attachment

Adds one or more attachments to an issue. Attachments are posted as multipart/form-data (RFC 1867).

Note that:

• The request must have a X-Atlassian-Token: no-check header, if not it is blocked. See Special headers for more information.
• The name of the multipart/form-data parameter that contains the attachments must be file.

The following examples upload a file called myfile.txt to the issue TEST-123:

curl

curl --location --request POST 'https://your-domain.atlassian.net/rest/api/2/issue/TEST-123/attachments'
 -u 'email@example.com:<api_token>'
 -H 'X-Atlassian-Token: no-check'
 --form 'file=@"myfile.txt"'

java

// This code sample uses the  'Unirest' library:
 // http://unirest.io/java.html
 HttpResponse response = Unirest.post("https://your-domain.atlassian.net/rest/api/2/issue/{issueIdOrKey}/attachments")
         .basicAuth("email@example.com", "")
         .header("Accept", "application/json")
         .header("X-Atlassian-Token", "no-check")
         .field("file", new File("myfile.txt"))
         .asJson();

         System.out.println(response.getBody());

转自：The Jira Cloud platform REST API