ActivityPub signature verification

Here’s the Actor object with a public key:

{
  "@context": [
    "https://www.w3.org/ns/activitystreams",
    "https://w3id.org/security/v1"
  ],
  "type": "Person",
  "id": "https://activitypub.academy/users/beguca_dedashul",
  "publicKey": {
    "id": "https://activitypub.academy/users/beguca_dedashul#main-key",
    "owner": "https://activitypub.academy/users/beguca_dedashul",
    "publicKeyPem": "-----BEGIN PUBLIC KEY-----
    MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAzOQXkYZN7LoATFNQ3mm/
    SeBxRiI0BKpoRLSELCZR9U4GcZ2wHGTENvc++3h63vgIVXzgjWHSaMj1w+LvG3c4
    JV4FrOFGzrxtQvyFDUyNmihRU2+cxqLQiKuZbUxrKFtyA6hdmiCi8IX41UZiA9QB
    hmXMP0REj/OSth0FS8+o8iMN4kB0Qvq9JSrIkV0Lwv3jJs/LP9QLjX5fgJUVTbdP
    pVus9AhLUJjZ3i/KIGehn9bbwg8PnEQOHuEO7lxO0YXetbv7+HQEV+jJAWY/5nJv
    FUTQTIOeGFa8FkdDgYwAxyXDzumrjY69DzXcXxkzro1spagh5wsRC08o3Cyi1mTm
    6QIDAQAB
    -----END PUBLIC KEY-----
    "
  },
  "following": "https://activitypub.academy/users/beguca_dedashul/following",
  "followers": "https://activitypub.academy/users/beguca_dedashul/followers",
  "inbox": "https://activitypub.academy/users/beguca_dedashul/inbox",
  "outbox": "https://activitypub.academy/users/beguca_dedashul/outbox",
  "featured": "https://activitypub.academy/users/beguca_dedashul/collections/featured",
  "featuredTags": "https://activitypub.academy/users/beguca_dedashul/collections/tags",
  "preferredUsername": "beguca_dedashul",
  "name": "Beguca Dedashul",
  "summary": "",
  "url": "https://activitypub.academy/@beguca_dedashul",
  "manuallyApprovesFollowers": "",
  "discoverable": "",
  "published": "2024-01-06T00:00:00Z",
  "devices": "https://activitypub.academy/users/beguca_dedashul/collections/devices",
  "tag": [],
  "attachment": [],
  "endpoints": { "sharedInbox": "https://activitypub.academy/inbox" }
}

Here is the request I’m attempting to verify:

POST /smolblog/v2/site/426a9e54-435f-4135-9252-0d0a6ddd1dba/activitypub/inbox HTTP/1.1
authorization: 
host: smol.blog
user-agent: http.rb/5.1.1 (Mastodon/4.1.4; +https://activitypub.academy/)
content-length: 469
accept-encoding: gzip
content-type: application/activity+json
date: Mon, 08 Jan 2024 01:42:32 GMT
digest: SHA-256=xKL37qOMyoMqV+0K06sABVDGVe0VNwbYuPukUOF6K1A=
signature: keyId="https://activitypub.academy/users/beguca_dedashul#main-key",algorithm="rsa-sha256",headers="(request-target) host date digest content-type",signature="i1BaPQGtKZ0J9EIeyLumVjWRPVh7RLEFUsrhQZz3hS6VTcQ4jY42Ff4AWL+zPStlJP4BDkdf8gjGt/IoKdYS2cnBKODAr2Ud/UjV/vwxAzguYPu1ZKb7ty0Xc2mAJ2prGLb1frzqBVJpAit95864VIe2xEAVgispsqG57qW8jjrHTrwnIOu5cQbjUA6oCKSub3j/X1lXxcKRIIaC9kRiNZc26YDdpdkA/xYlItw63+1GjtdbWP0c3BpMsCAd+Mkji3OjwOU2NZXbM1uG6c/XVtcq+MlLsFe99RDLRNXqlw831e0LThh3kOKnQ8uHHnGBVHkzyba9OtC0TB/9vF3D1A=="
x-forwarded-host: smol.blog
x-forwarded-proto: https

{"@context":"https://www.w3.org/ns/activitystreams","id":"https://activitypub.academy/users/beguca_dedashul#follows/1706/undo","type":"Undo","actor":"https://activitypub.academy/users/beguca_dedashul","object":{"id":"https://activitypub.academy/240f28cc-0cc0-457f-8bb9-1ee4c3ec3579","type":"Follow","actor":"https://activitypub.academy/users/beguca_dedashul","object":"https://smol.blog/wp-json/smolblog/v2/site/426a9e54-435f-4135-9252-0d0a6ddd1dba/activitypub/actor"}}"
Evan Hildreth @oddevan