Google Fonts APIからWOFF2対応のスタイルシート（CSS）をGETする

Google Fonts APIで返されるスタイルシートはユーザーエージェントで内容が変わる

普通にGETするとtruetypeで返ってくる

$ curl 'https://fonts.googleapis.com/css2?family=Roboto+Flex:opsz,wght@8..144,100..1000&display=swap'
@font-face {
  font-family: 'Roboto Flex';
  font-style: normal;
  font-weight: 400;
  font-stretch: normal;
  font-display: swap;
  src: url(https://fonts.gstatic.com/s/robotoflex/v26/NaNnepOXO_NexZs0b5QrzlOHb8wCikXpYqmZsWI-__OGbt8jZktqc2V3Zs0KvDLdBP8SBZtOs2IifRuUZQMsPJtUsR4DEK6cULNeUx9XgTnH37Ha_FIAp4Fm0PP1hw45DntW2x0wZGzhPmr1YNMYKYn9_1IQXGwJAiUJVUMdN5YUW4O8HtSoXjC1z3QSabshNFVe3e0O5j3ZjrZCu23Qd4G0EBysQNK-QKavMl1cKq3tHXtXi8mzLjaAQbE.ttf) format('truetype');
}

ユーザーエージェントのヘッダーを付けてやるとwoff2対応で返ってくる

$ curl 'https://fonts.googleapis.com/css2?family=Noto+Sans+JP:wght@100..900&family=Roboto+Flex:opsz,wght@8..144,100..1000&display=swap' \  
  -H 'user-agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/128.0.0.0 Safari/537.36'
/* cyrillic-ext */
@font-face {
  font-family: 'Roboto Flex';
  font-style: normal;
  font-weight: 100 1000;
  font-stretch: 100%;
  font-display: swap;
  src: url(https://fonts.gstatic.com/s/robotoflex/v26/NaNNepOXO_NexZs0b5QrzlOHb8wCikXpYqmZsWI-__OGbt8jZktqc2V3Zs0KvDLdBP8SBZtOs2IifRuUZQMsPJtUsR4DEK6cULNeUx9XgTnH37Ha_FIAp4Fm0PP1hw45DntW2x0wZGzhPmr1YNMYKYn9_1IQXGwJAiUJVUMdN5YUW4O8HtSoXjC79QRyaLshNDUf3e0O-gn5rrZCu20YNau1OPF80A.woff2) format('woff2');
  unicode-range: U+0460-052F, U+1C80-1C88, U+20B4, U+2DE0-2DFF, U+A640-A69F, U+FE2E-FE2F;
}
/* cyrillic */
@font-face {
  font-family: 'Roboto Flex';
  font-style: normal;
  font-weight: 100 1000;
  font-stretch: 100%;
  font-display: swap;
  src: url(https://fonts.gstatic.com/s/robotoflex/v26/NaNNepOXO_NexZs0b5QrzlOHb8wCikXpYqmZsWI-__OGbt8jZktqc2V3Zs0KvDLdBP8SBZtOs2IifRuUZQMsPJtUsR4DEK6cULNeUx9XgTnH37Ha_FIAp4Fm0PP1hw45DntW2x0wZGzhPmr1YNMYKYn9_1IQXGwJAiUJVUMdN5YUW4O8HtSoXjC79QRyaLshNDUf3e0O-gn5rrZCu20YNau8OPF80A.woff2) format('woff2');
  unicode-range: U+0301, U+0400-045F, U+0490-0491, U+04B0-04B1, U+2116;
}
/* greek */
@font-face {
  font-family: 'Roboto Flex';
  font-style: normal;
  font-weight: 100 1000;
  font-stretch: 100%;
  font-display: swap;
  src: url(https://fonts.gstatic.com/s/robotoflex/v26/NaNNepOXO_NexZs0b5QrzlOHb8wCikXpYqmZsWI-__OGbt8jZktqc2V3Zs0KvDLdBP8SBZtOs2IifRuUZQMsPJtUsR4DEK6cULNeUx9XgTnH37Ha_FIAp4Fm0PP1hw45DntW2x0wZGzhPmr1YNMYKYn9_1IQXGwJAiUJVUMdN5YUW4O8HtSoXjC79QRyaLshNDUf3e0O-gn5rrZCu20YNau7OPF80A.woff2) format('woff2');
  unicode-range: U+0370-0377, U+037A-037F, U+0384-038A, U+038C, U+038E-03A1, U+03A3-03FF;
}
/* vietnamese */
@font-face {
  font-family: 'Roboto Flex';
  font-style: normal;
  font-weight: 100 1000;
  font-stretch: 100%;
  font-display: swap;
  src: url(https://fonts.gstatic.com/s/robotoflex/v26/NaNNepOXO_NexZs0b5QrzlOHb8wCikXpYqmZsWI-__OGbt8jZktqc2V3Zs0KvDLdBP8SBZtOs2IifRuUZQMsPJtUsR4DEK6cULNeUx9XgTnH37Ha_FIAp4Fm0PP1hw45DntW2x0wZGzhPmr1YNMYKYn9_1IQXGwJAiUJVUMdN5YUW4O8HtSoXjC79QRyaLshNDUf3e0O-gn5rrZCu20YNau3OPF80A.woff2) format('woff2');
  unicode-range: U+0102-0103, U+0110-0111, U+0128-0129, U+0168-0169, U+01A0-01A1, U+01AF-01B0, U+0300-0301, U+0303-0304, U+0308-0309, U+0323, U+0329, U+1EA0-1EF9, U+20AB;
}
/* latin-ext */
@font-face {
  font-family: 'Roboto Flex';
  font-style: normal;
  font-weight: 100 1000;
  font-stretch: 100%;
  font-display: swap;
  src: url(https://fonts.gstatic.com/s/robotoflex/v26/NaNNepOXO_NexZs0b5QrzlOHb8wCikXpYqmZsWI-__OGbt8jZktqc2V3Zs0KvDLdBP8SBZtOs2IifRuUZQMsPJtUsR4DEK6cULNeUx9XgTnH37Ha_FIAp4Fm0PP1hw45DntW2x0wZGzhPmr1YNMYKYn9_1IQXGwJAiUJVUMdN5YUW4O8HtSoXjC79QRyaLshNDUf3e0O-gn5rrZCu20YNau2OPF80A.woff2) format('woff2');
  unicode-range: U+0100-02AF, U+0304, U+0308, U+0329, U+1E00-1E9F, U+1EF2-1EFF, U+2020, U+20A0-20AB, U+20AD-20C0, U+2113, U+2C60-2C7F, U+A720-A7FF;
}
/* latin */
@font-face {
  font-family: 'Roboto Flex';
  font-style: normal;
  font-weight: 100 1000;
  font-stretch: 100%;
  font-display: swap;
  src: url(https://fonts.gstatic.com/s/robotoflex/v26/NaNNepOXO_NexZs0b5QrzlOHb8wCikXpYqmZsWI-__OGbt8jZktqc2V3Zs0KvDLdBP8SBZtOs2IifRuUZQMsPJtUsR4DEK6cULNeUx9XgTnH37Ha_FIAp4Fm0PP1hw45DntW2x0wZGzhPmr1YNMYKYn9_1IQXGwJAiUJVUMdN5YUW4O8HtSoXjC79QRyaLshNDUf3e0O-gn5rrZCu20YNau4OPE.woff2) format('woff2');
  unicode-range: U+0000-00FF, U+0131, U+0152-0153, U+02BB-02BC, U+02C6, U+02DA, U+02DC, U+0304, U+0308, U+0329, U+2000-206F, U+2074, U+20AC, U+2122, U+2191, U+2193, U+2212, U+2215, U+FEFF, U+FFFD;
}