Allow to set a custom user agent

[raphaelm]

Apparently, some SMP providers out there block "python-requests" as a user agent, I assume because it is contained in popular default WAF blocklists. Example:

In [19]: requests.get("https://smp.soluz.io/iso6523-actorid-upis::0208:0123456", headers={"User-Agent": "python-requests"})
send: b'CONNECT smp.soluz.io:443 HTTP/1.0\r\n\r\n'
send: b'GET /iso6523-actorid-upis::0208:0123456 HTTP/1.1\r\nHost: smp.soluz.io\r\nUser-Agent: python-requests\r\nAccept-Encoding: gzip, deflate\r\nAccept: */*\r\nConnection: keep-alive\r\n\r\n'
reply: 'HTTP/1.1 403 Forbidden\r\n'
header: Server: Microsoft-Azure-Application-Gateway/v2
header: Date: Tue, 10 Mar 2026 08:37:38 GMT
header: Content-Type: text/html
header: Content-Length: 179
header: Connection: keep-alive
Out[19]: <Response [403]>

Changing the user agent is the quickest and also cleanest solution:

In [18]: requests.get("https://smp.soluz.io/iso6523-actorid-upis::0208:0123456", headers={"User-Agent": "peppol-py"})
send: b'CONNECT smp.soluz.io:443 HTTP/1.0\r\n\r\n'
send: b'GET /iso6523-actorid-upis::0208:0123456 HTTP/1.1\r\nHost: smp.soluz.io\r\nUser-Agent: peppol-py\r\nAccept-Encoding: gzip, deflate\r\nAccept: */*\r\nConnection: keep-alive\r\n\r\n'
reply: 'HTTP/1.1 404 Not Found\r\n'
header: Date: Tue, 10 Mar 2026 08:37:31 GMT
header: Content-Type: application/json; charset=utf-8
header: Content-Length: 123
header: Connection: keep-alive
header: Server: Microsoft-HTTPAPI/2.0
Out[18]: <Response [404]>

The example is 404 instead of 200 because I did not want to include an actual participant ID in this commit message.

[arj03]

Thanks