SPDX license info from `requirements.txt`

Hi,

I am using requirements.txt to generate bom file. And the output is as follows. I would like to know how can I get the SPDX license id generated? thanks!

output:
```

2022-05-10T10:55:22.184404+00:00


CycloneDX
cyclonedx-bom
3.2.1


CycloneDX
cyclonedx-python-lib
2.3.0


https://github.com/CycloneDX/cyclonedx-python-lib/issues


https://cyclonedx.org


https://github.com/CycloneDX/cyclonedx-python-lib/actions


https://github.com/CycloneDX/cyclonedx-python-lib/blob/main/CHANGELOG.md


https://pypi.org/project/cyclonedx-python-lib/


https://github.com/CycloneDX/cyclonedx-python-lib/blob/main/LICENSE


https://cyclonedx.github.io/cyclonedx-python-lib/


https://github.com/CycloneDX/cyclonedx-python-lib







backports.entry-points-selectable
1.1.0
pkg:pypi/backports.entry-points-selectable@1.1.0


mypy-extensions
0.4.3
pkg:pypi/mypy-extensions@0.4.3


mccabe
0.6.1
pkg:pypi/mccabe@0.6.1


python-dateutil
2.8.1
pkg:pypi/python-dateutil@2.8.1


filelock
3.0.12
pkg:pypi/filelock@3.0.12


certifi
2021.5.30
pkg:pypi/certifi@2021.5.30


py
1.10.0
pkg:pypi/py@1.10.0


pydantic
1.8.2
pkg:pypi/pydantic@1.8.2


black
21.9b0
pkg:pypi/black@21.9b0


pytest
6.2.5
pkg:pypi/pytest@6.2.5


chardet
4.0.0
pkg:pypi/chardet@4.0.0


python-docx
0.8.11
pkg:pypi/python-docx@0.8.11


protobuf
3.17.2
pkg:pypi/protobuf@3.17.2


pyflakes
2.2.0
pkg:pypi/pyflakes@2.2.0


boto3
1.18.10
pkg:pypi/boto3@1.18.10


starlette
0.14.2
pkg:pypi/starlette@0.14.2


pycparser
2.20
pkg:pypi/pycparser@2.20


s3transfer
0.5.0
pkg:pypi/s3transfer@0.5.0


pyparsing
2.4.7
pkg:pypi/pyparsing@2.4.7


distlib
0.3.2
pkg:pypi/distlib@0.3.2


charset-normalizer
2.0.4
pkg:pypi/charset-normalizer@2.0.4


python-multipart
0.0.5
pkg:pypi/python-multipart@0.0.5


ddtrace
0.49.2
pkg:pypi/ddtrace@0.49.2


pytest-mock
3.6.1
pkg:pypi/pytest-mock@3.6.1


pytest-cov
2.12.1
pkg:pypi/pytest-cov@2.12.1


tenacity
7.0.0
pkg:pypi/tenacity@7.0.0


pymongo
3.11.4
pkg:pypi/pymongo@3.11.4


tox
3.24.3
pkg:pypi/tox@3.24.3


virtualenv
20.7.2
pkg:pypi/virtualenv@20.7.2


mangum
0.11.0
pkg:pypi/mangum@0.11.0


platformdirs
2.3.0
pkg:pypi/platformdirs@2.3.0


aiofiles
0.7.0
pkg:pypi/aiofiles@0.7.0


iniconfig
1.1.1
pkg:pypi/iniconfig@1.1.1


attrs
21.2.0
pkg:pypi/attrs@21.2.0


requests
2.25.1
pkg:pypi/requests@2.25.1


urllib3
1.26.5
pkg:pypi/urllib3@1.26.5


tomli
1.2.1
pkg:pypi/tomli@1.2.1


cryptography
3.4.7
pkg:pypi/cryptography@3.4.7


jmespath
0.10.0
pkg:pypi/jmespath@0.10.0


toml
0.10.2
pkg:pypi/toml@0.10.2


typing-extensions
3.10.0.0
pkg:pypi/typing-extensions@3.10.0.0


cachetools
4.2.2
pkg:pypi/cachetools@4.2.2


fastapi
0.65.1
pkg:pypi/fastapi@0.65.1


PyJWT
2.1.0
pkg:pypi/pyjwt@2.1.0


flake9
3.8.3.post2
pkg:pypi/flake9@3.8.3.post2


pycodestyle
2.6.0
pkg:pypi/pycodestyle@2.6.0


isort
5.9.3
pkg:pypi/isort@5.9.3


idna
2.10
pkg:pypi/idna@2.10


packaging
20.9
pkg:pypi/packaging@20.9


coverage
5.5
pkg:pypi/coverage@5.5


six
1.16.0
pkg:pypi/six@1.16.0


botocore
1.21.14
pkg:pypi/botocore@1.21.14


cffi
1.14.5
pkg:pypi/cffi@1.14.5


click
8.0.1
pkg:pypi/click@8.0.1


regex
2021.8.28
pkg:pypi/regex@2021.8.28


pathspec
0.9.0
pkg:pypi/pathspec@0.9.0


lxml
4.6.3
pkg:pypi/lxml@4.6.3


pluggy
1.0.0
pkg:pypi/pluggy@1.0.0


autoflake
1.4
pkg:pypi/autoflake@1.4

```

expected content included:
```
"license": {
"id": "Apache-2.0",
"text": {
"contentType": "text/plain",
"encoding": "base64",
```